Merge branch 'ptrace' of git://git.kernel.org/pub/scm/linux/kernel/git/oleg/misc

* 'ptrace' of git://git.kernel.org/pub/scm/linux/kernel/git/oleg/misc: (41 commits)
  signal: trivial, fix the "timespec declared inside parameter list" warning
  job control: reorganize wait_task_stopped()
  ptrace: fix signal->wait_chldexit usage in task_clear_group_stop_trapping()
  signal: sys_sigprocmask() needs retarget_shared_pending()
  signal: cleanup sys_sigprocmask()
  signal: rename signandsets() to sigandnsets()
  signal: do_sigtimedwait() needs retarget_shared_pending()
  signal: introduce do_sigtimedwait() to factor out compat/native code
  signal: sys_rt_sigtimedwait: simplify the timeout logic
  signal: cleanup sys_rt_sigprocmask()
  x86: signal: sys_rt_sigreturn() should use set_current_blocked()
  x86: signal: handle_signal() should use set_current_blocked()
  signal: sigprocmask() should do retarget_shared_pending()
  signal: sigprocmask: narrow the scope of ->siglock
  signal: retarget_shared_pending: optimize while_each_thread() loop
  signal: retarget_shared_pending: consider shared/unblocked signals only
  signal: introduce retarget_shared_pending()
  ptrace: ptrace_check_attach() should not do s/STOPPED/TRACED/
  signal: Turn SIGNAL_STOP_DEQUEUED into GROUP_STOP_DEQUEUED
  signal: do_signal_stop: Remove the unneeded task_clear_group_stop_pending()
  ...

9 files changed, 659 insertions, 366 deletions

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 4fd173cd8e5..40a24932a8a 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -601,10 +601,7 @@ long sys_rt_sigreturn(struct pt_regs *regs)
 		goto badframe;
 
 	sigdelsetmask(&set, ~_BLOCKABLE);
-	spin_lock_irq(&current->sighand->siglock);
-	current->blocked = set;
-	recalc_sigpending();
-	spin_unlock_irq(&current->sighand->siglock);
+	set_current_blocked(&set);
 
 	if (restore_sigcontext(regs, &frame->uc.uc_mcontext, &ax))
 		goto badframe;
@@ -682,6 +679,7 @@ static int
 handle_signal(unsigned long sig, siginfo_t *info, struct k_sigaction *ka,
 	      sigset_t *oldset, struct pt_regs *regs)
 {
+	sigset_t blocked;
 	int ret;
 
 	/* Are we from a system call? */
@@ -741,12 +739,10 @@ handle_signal(unsigned long sig, siginfo_t *info, struct k_sigaction *ka,
 	 */
 	regs->flags &= ~X86_EFLAGS_TF;
 
-	spin_lock_irq(&current->sighand->siglock);
-	sigorsets(&current->blocked, &current->blocked, &ka->sa.sa_mask);
+	sigorsets(&blocked, &current->blocked, &ka->sa.sa_mask);
 	if (!(ka->sa.sa_flags & SA_NODEFER))
-		sigaddset(&current->blocked, sig);
-	recalc_sigpending();
-	spin_unlock_irq(&current->sighand->siglock);
+		sigaddset(&blocked, sig);
+	set_current_blocked(&blocked);
 
 	tracehook_signal_handler(sig, info, ka, regs,
 				 test_thread_flag(TIF_SINGLESTEP));
diff --git a/fs/exec.c b/fs/exec.c
index 5e62d26a4fe..8328beb9016 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1659,6 +1659,7 @@ static int zap_process(struct task_struct *start, int exit_code)
 
 	t = start;
 	do {
+		task_clear_group_stop_pending(t);
 		if (t != current && t->mm) {
 			sigaddset(&t->pending.signal, SIGKILL);
 			signal_wake_up(t, 1);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 12211e1666e..885c4f242ad 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -653,9 +653,8 @@ struct signal_struct {
  * Bits in flags field of signal_struct.
  */
 #define SIGNAL_STOP_STOPPED	0x00000001 /* job control stop in effect */
-#define SIGNAL_STOP_DEQUEUED	0x00000002 /* stop signal dequeued */
-#define SIGNAL_STOP_CONTINUED	0x00000004 /* SIGCONT since WCONTINUED reap */
-#define SIGNAL_GROUP_EXIT	0x00000008 /* group exit in progress */
+#define SIGNAL_STOP_CONTINUED	0x00000002 /* SIGCONT since WCONTINUED reap */
+#define SIGNAL_GROUP_EXIT	0x00000004 /* group exit in progress */
 /*
  * Pending notifications to parent.
  */
@@ -1251,6 +1250,7 @@ struct task_struct {
 	int exit_state;
 	int exit_code, exit_signal;
 	int pdeath_signal;  /*  The signal sent when the parent dies  */
+	unsigned int group_stop;	/* GROUP_STOP_*, siglock protected */
 	/* ??? */
 	unsigned int personality;
 	unsigned did_exec:1;
@@ -1771,6 +1771,17 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *
 #define tsk_used_math(p) ((p)->flags & PF_USED_MATH)
 #define used_math() tsk_used_math(current)
 
+/*
+ * task->group_stop flags
+ */
+#define GROUP_STOP_SIGMASK	0xffff    /* signr of the last group stop */
+#define GROUP_STOP_PENDING	(1 << 16) /* task should stop for group stop */
+#define GROUP_STOP_CONSUME	(1 << 17) /* consume group stop count */
+#define GROUP_STOP_TRAPPING	(1 << 18) /* switching from STOPPED to TRACED */
+#define GROUP_STOP_DEQUEUED	(1 << 19) /* stop signal dequeued */
+
+extern void task_clear_group_stop_pending(struct task_struct *task);
+
 #ifdef CONFIG_PREEMPT_RCU
 
 #define RCU_READ_UNLOCK_BLOCKED (1 << 0) /* blocked while in RCU read-side. */
diff --git a/include/linux/signal.h b/include/linux/signal.h
index 29a68ac7af8..a822300a253 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -125,13 +125,13 @@ _SIG_SET_BINOP(sigorsets, _sig_or)
 #define _sig_and(x,y)	((x) & (y))
 _SIG_SET_BINOP(sigandsets, _sig_and)
 
-#define _sig_nand(x,y)	((x) & ~(y))
-_SIG_SET_BINOP(signandsets, _sig_nand)
+#define _sig_andn(x,y)	((x) & ~(y))
+_SIG_SET_BINOP(sigandnsets, _sig_andn)
 
 #undef _SIG_SET_BINOP
 #undef _sig_or
 #undef _sig_and
-#undef _sig_nand
+#undef _sig_andn
 
 #define _SIG_SET_OP(name, op)						\
 static inline void name(sigset_t *set)					\
@@ -236,6 +236,9 @@ static inline int valid_signal(unsigned long sig)
 	return sig <= _NSIG ? 1 : 0;
 }
 
+struct timespec;
+struct pt_regs;
+
 extern int next_signal(struct sigpending *pending, sigset_t *mask);
 extern int do_send_sig_info(int sig, struct siginfo *info,
 				struct task_struct *p, bool group);
@@ -244,10 +247,12 @@ extern int __group_send_sig_info(int, struct siginfo *, struct task_struct *);
 extern long do_rt_tgsigqueueinfo(pid_t tgid, pid_t pid, int sig,
 				 siginfo_t *info);
 extern long do_sigpending(void __user *, unsigned long);
+extern int do_sigtimedwait(const sigset_t *, siginfo_t *,
+				const struct timespec *);
 extern int sigprocmask(int, sigset_t *, sigset_t *);
+extern void set_current_blocked(const sigset_t *);
 extern int show_unhandled_signals;
 
-struct pt_regs;
 extern int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka, struct pt_regs *regs, void *cookie);
 extern void exit_signals(struct task_struct *tsk);
 
diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index ebcfa4ebdbf..e95f5236611 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -469,33 +469,6 @@ static inline int tracehook_get_signal(struct task_struct *task,
 }
 
 /**
- * tracehook_notify_jctl - report about job control stop/continue
- * @notify:		zero, %CLD_STOPPED or %CLD_CONTINUED
- * @why:		%CLD_STOPPED or %CLD_CONTINUED
- *
- * This is called when we might call do_notify_parent_cldstop().
- *
- * @notify is zero if we would not ordinarily send a %SIGCHLD,
- * or is the %CLD_STOPPED or %CLD_CONTINUED .si_code for %SIGCHLD.
- *
- * @why is %CLD_STOPPED when about to stop for job control;
- * we are already in %TASK_STOPPED state, about to call schedule().
- * It might also be that we have just exited (check %PF_EXITING),
- * but need to report that a group-wide stop is complete.
- *
- * @why is %CLD_CONTINUED when waking up after job control stop and
- * ready to make a delayed @notify report.
- *
- * Return the %CLD_* value for %SIGCHLD, or zero to generate no signal.
- *
- * Called with the siglock held.
- */
-static inline int tracehook_notify_jctl(int notify, int why)
-{
-	return notify ?: (current->ptrace & PT_PTRACED) ? why : 0;
-}
-
-/**
  * tracehook_finish_jctl - report about return from job control stop
  *
  * This is called by do_signal_stop() after wakeup.
diff --git a/kernel/compat.c b/kernel/compat.c
index 38b1d2c1cbe..9214dcd087b 100644
--- a/kernel/compat.c
+++ b/kernel/compat.c
@@ -890,10 +890,9 @@ compat_sys_rt_sigtimedwait (compat_sigset_t __user *uthese,
 {
 	compat_sigset_t s32;
 	sigset_t s;
-	int sig;
 	struct timespec t;
 	siginfo_t info;
-	long ret, timeout = 0;
+	long ret;
 
 	if (sigsetsize != sizeof(sigset_t))
 		return -EINVAL;
@@ -901,51 +900,19 @@ compat_sys_rt_sigtimedwait (compat_sigset_t __user *uthese,
 	if (copy_from_user(&s32, uthese, sizeof(compat_sigset_t)))
 		return -EFAULT;
 	sigset_from_compat(&s, &s32);
-	sigdelsetmask(&s,sigmask(SIGKILL)|sigmask(SIGSTOP));
-	signotset(&s);
 
 	if (uts) {
-		if (get_compat_timespec (&t, uts))
+		if (get_compat_timespec(&t, uts))
 			return -EFAULT;
-		if (t.tv_nsec >= 1000000000L || t.tv_nsec < 0
-				|| t.tv_sec < 0)
-			return -EINVAL;
 	}
 
-	spin_lock_irq(&current->sighand->siglock);
-	sig = dequeue_signal(current, &s, &info);
-	if (!sig) {
-		timeout = MAX_SCHEDULE_TIMEOUT;
-		if (uts)
-			timeout = timespec_to_jiffies(&t)
-				+(t.tv_sec || t.tv_nsec);
-		if (timeout) {
-			current->real_blocked = current->blocked;
-			sigandsets(&current->blocked, &current->blocked, &s);
-
-			recalc_sigpending();
-			spin_unlock_irq(&current->sighand->siglock);
-
-			timeout = schedule_timeout_interruptible(timeout);
-
-			spin_lock_irq(&current->sighand->siglock);
-			sig = dequeue_signal(current, &s, &info);
-			current->blocked = current->real_blocked;
-			siginitset(&current->real_blocked, 0);
-			recalc_sigpending();
-		}
-	}
-	spin_unlock_irq(&current->sighand->siglock);
+	ret = do_sigtimedwait(&s, &info, uts ? &t : NULL);
 
-	if (sig) {
-		ret = sig;
-		if (uinfo) {
-			if (copy_siginfo_to_user32(uinfo, &info))
-				ret = -EFAULT;
-		}
-	}else {
-		ret = timeout?-EINTR:-EAGAIN;
+	if (ret > 0 && uinfo) {
+		if (copy_siginfo_to_user32(uinfo, &info))
+			ret = -EFAULT;
 	}
+
 	return ret;
 
 }
diff --git a/kernel/exit.c b/kernel/exit.c
index 8dd87418154..20a40647152 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1377,11 +1377,23 @@ static int *task_stopped_code(struct task_struct *p, bool ptrace)
 	return NULL;
 }
 
-/*
- * Handle sys_wait4 work for one task in state TASK_STOPPED.  We hold
- * read_lock(&tasklist_lock) on entry.  If we return zero, we still hold
- * the lock and this task is uninteresting.  If we return nonzero, we have
- * released the lock and the system call should return.
+/**
+ * wait_task_stopped - Wait for %TASK_STOPPED or %TASK_TRACED
+ * @wo: wait options
+ * @ptrace: is the wait for ptrace
+ * @p: task to wait for
+ *
+ * Handle sys_wait4() work for %p in state %TASK_STOPPED or %TASK_TRACED.
+ *
+ * CONTEXT:
+ * read_lock(&tasklist_lock), which is released if return value is
+ * non-zero.  Also, grabs and releases @p->sighand->siglock.
+ *
+ * RETURNS:
+ * 0 if wait condition didn't exist and search for other wait conditions
+ * should continue.  Non-zero return, -errno on failure and @p's pid on
+ * success, implies that tasklist_lock is released and wait condition
+ * search should terminate.
  */
 static int wait_task_stopped(struct wait_opts *wo,
 				int ptrace, struct task_struct *p)
@@ -1397,6 +1409,9 @@ static int wait_task_stopped(struct wait_opts *wo,
 	if (!ptrace && !(wo->wo_flags & WUNTRACED))
 		return 0;
 
+	if (!task_stopped_code(p, ptrace))
+		return 0;
+
 	exit_code = 0;
 	spin_lock_irq(&p->sighand->siglock);
 
@@ -1538,33 +1553,84 @@ static int wait_consider_task(struct wait_opts *wo, int ptrace,
 		return 0;
 	}
 
-	if (likely(!ptrace) && unlikely(task_ptrace(p))) {
+	/* dead body doesn't have much to contribute */
+	if (p->exit_state == EXIT_DEAD)
+		return 0;
+
+	/* slay zombie? */
+	if (p->exit_state == EXIT_ZOMBIE) {
+		/*
+		 * A zombie ptracee is only visible to its ptracer.
+		 * Notification and reaping will be cascaded to the real
+		 * parent when the ptracer detaches.
+		 */
+		if (likely(!ptrace) && unlikely(task_ptrace(p))) {
+			/* it will become visible, clear notask_error */
+			wo->notask_error = 0;
+			return 0;
+		}
+
+		/* we don't reap group leaders with subthreads */
+		if (!delay_group_leader(p))
+			return wait_task_zombie(wo, p);
+
 		/*
-		 * This child is hidden by ptrace.
-		 * We aren't allowed to see it now, but eventually we will.
+		 * Allow access to stopped/continued state via zombie by
+		 * falling through.  Clearing of notask_error is complex.
+		 *
+		 * When !@ptrace:
+		 *
+		 * If WEXITED is set, notask_error should naturally be
+		 * cleared.  If not, subset of WSTOPPED|WCONTINUED is set,
+		 * so, if there are live subthreads, there are events to
+		 * wait for.  If all subthreads are dead, it's still safe
+		 * to clear - this function will be called again in finite
+		 * amount time once all the subthreads are released and
+		 * will then return without clearing.
+		 *
+		 * When @ptrace:
+		 *
+		 * Stopped state is per-task and thus can't change once the
+		 * target task dies.  Only continued and exited can happen.
+		 * Clear notask_error if WCONTINUED | WEXITED.
+		 */
+		if (likely(!ptrace) || (wo->wo_flags & (WCONTINUED | WEXITED)))
+			wo->notask_error = 0;
+	} else {
+		/*
+		 * If @p is ptraced by a task in its real parent's group,
+		 * hide group stop/continued state when looking at @p as
+		 * the real parent; otherwise, a single stop can be
+		 * reported twice as group and ptrace stops.
+		 *
+		 * If a ptracer wants to distinguish the two events for its
+		 * own children, it should create a separate process which
+		 * takes the role of real parent.
+		 */
+		if (likely(!ptrace) && task_ptrace(p) &&
+		    same_thread_group(p->parent, p->real_parent))
+			return 0;
+
+		/*
+		 * @p is alive and it's gonna stop, continue or exit, so
+		 * there always is something to wait for.
 		 */
 		wo->notask_error = 0;
-		return 0;
 	}
 
-	if (p->exit_state == EXIT_DEAD)
-		return 0;
-
 	/*
-	 * We don't reap group leaders with subthreads.
+	 * Wait for stopped.  Depending on @ptrace, different stopped state
+	 * is used and the two don't interact with each other.
 	 */
-	if (p->exit_state == EXIT_ZOMBIE && !delay_group_leader(p))
-		return wait_task_zombie(wo, p);
+	ret = wait_task_stopped(wo, ptrace, p);
+	if (ret)
+		return ret;
 
 	/*
-	 * It's stopped or running now, so it might
-	 * later continue, exit, or stop again.
+	 * Wait for continued.  There's only one continued state and the
+	 * ptracer can consume it which can confuse the real parent.  Don't
+	 * use WCONTINUED from ptracer.  You don't need or want it.
 	 */
-	wo->notask_error = 0;
-
-	if (task_stopped_code(p, ptrace))
-		return wait_task_stopped(wo, ptrace, p);
-
 	return wait_task_continued(wo, p);
 }
 
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index dc7ab65f3b3..7a81fc07134 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -38,35 +38,33 @@ void __ptrace_link(struct task_struct *child, struct task_struct *new_parent)
 	child->parent = new_parent;
 }
 
-/*
- * Turn a tracing stop into a normal stop now, since with no tracer there
- * would be no way to wake it up with SIGCONT or SIGKILL.  If there was a
- * signal sent that would resume the child, but didn't because it was in
- * TASK_TRACED, resume it now.
- * Requires that irqs be disabled.
- */
-static void ptrace_untrace(struct task_struct *child)
-{
-	spin_lock(&child->sighand->siglock);
-	if (task_is_traced(child)) {
-		/*
-		 * If the group stop is completed or in progress,
-		 * this thread was already counted as stopped.
-		 */
-		if (child->signal->flags & SIGNAL_STOP_STOPPED ||
-		    child->signal->group_stop_count)
-			__set_task_state(child, TASK_STOPPED);
-		else
-			signal_wake_up(child, 1);
-	}
-	spin_unlock(&child->sighand->siglock);
-}
-
-/*
- * unptrace a task: move it back to its original parent and
- * remove it from the ptrace list.
+/**
+ * __ptrace_unlink - unlink ptracee and restore its execution state
+ * @child: ptracee to be unlinked
  *
- * Must be called with the tasklist lock write-held.
+ * Remove @child from the ptrace list, move it back to the original parent,
+ * and restore the execution state so that it conforms to the group stop
+ * state.
+ *
+ * Unlinking can happen via two paths - explicit PTRACE_DETACH or ptracer
+ * exiting.  For PTRACE_DETACH, unless the ptracee has been killed between
+ * ptrace_check_attach() and here, it's guaranteed to be in TASK_TRACED.
+ * If the ptracer is exiting, the ptracee can be in any state.
+ *
+ * After detach, the ptracee should be in a state which conforms to the
+ * group stop.  If the group is stopped or in the process of stopping, the
+ * ptracee should be put into TASK_STOPPED; otherwise, it should be woken
+ * up from TASK_TRACED.
+ *
+ * If the ptracee is in TASK_TRACED and needs to be moved to TASK_STOPPED,
+ * it goes through TRACED -> RUNNING -> STOPPED transition which is similar
+ * to but in the opposite direction of what happens while attaching to a
+ * stopped task.  However, in this direction, the intermediate RUNNING
+ * state is not hidden even from the current ptracer and if it immediately
+ * re-attaches and performs a WNOHANG wait(2), it may fail.
+ *
+ * CONTEXT:
+ * write_lock_irq(tasklist_lock)
  */
 void __ptrace_unlink(struct task_struct *child)
 {
@@ -76,8 +74,27 @@ void __ptrace_unlink(struct task_struct *child)
 	child->parent = child->real_parent;
 	list_del_init(&child->ptrace_entry);
 
-	if (task_is_traced(child))
-		ptrace_untrace(child);
+	spin_lock(&child->sighand->siglock);
+
+	/*
+	 * Reinstate GROUP_STOP_PENDING if group stop is in effect and
+	 * @child isn't dead.
+	 */
+	if (!(child->flags & PF_EXITING) &&
+	    (child->signal->flags & SIGNAL_STOP_STOPPED ||
+	     child->signal->group_stop_count))
+		child->group_stop |= GROUP_STOP_PENDING;
+
+	/*
+	 * If transition to TASK_STOPPED is pending or in TASK_TRACED, kick
+	 * @child in the butt.  Note that @resume should be used iff @child
+	 * is in TASK_TRACED; otherwise, we might unduly disrupt
+	 * TASK_KILLABLE sleeps.
+	 */
+	if (child->group_stop & GROUP_STOP_PENDING || task_is_traced(child))
+		signal_wake_up(child, task_is_traced(child));
+
+	spin_unlock(&child->sighand->siglock);
 }
 
 /*
@@ -96,16 +113,14 @@ int ptrace_check_attach(struct task_struct *child, int kill)
 	 */
 	read_lock(&tasklist_lock);
 	if ((child->ptrace & PT_PTRACED) && child->parent == current) {
-		ret = 0;
 		/*
 		 * child->sighand can't be NULL, release_task()
 		 * does ptrace_unlink() before __exit_signal().
 		 */
 		spin_lock_irq(&child->sighand->siglock);
-		if (task_is_stopped(child))
-			child->state = TASK_TRACED;
-		else if (!task_is_traced(child) && !kill)
-			ret = -ESRCH;
+		WARN_ON_ONCE(task_is_stopped(child));
+		if (task_is_traced(child) || kill)
+			ret = 0;
 		spin_unlock_irq(&child->sighand->siglock);
 	}
 	read_unlock(&tasklist_lock);
@@ -169,6 +184,7 @@ bool ptrace_may_access(struct task_struct *task, unsigned int mode)
 
 static int ptrace_attach(struct task_struct *task)
 {
+	bool wait_trap = false;
 	int retval;
 
 	audit_ptrace(task);
@@ -208,12 +224,42 @@ static int ptrace_attach(struct task_struct *task)
 	__ptrace_link(task, current);
 	send_sig_info(SIGSTOP, SEND_SIG_FORCED, task);
 
+	spin_lock(&task->sighand->siglock);
+
+	/*
+	 * If the task is already STOPPED, set GROUP_STOP_PENDING and
+	 * TRAPPING, and kick it so that it transits to TRACED.  TRAPPING
+	 * will be cleared if the child completes the transition or any
+	 * event which clears the group stop states happens.  We'll wait
+	 * for the transition to complete before returning from this
+	 * function.
+	 *
+	 * This hides STOPPED -> RUNNING -> TRACED transition from the
+	 * attaching thread but a different thread in the same group can
+	 * still observe the transient RUNNING state.  IOW, if another
+	 * thread's WNOHANG wait(2) on the stopped tracee races against
+	 * ATTACH, the wait(2) may fail due to the transient RUNNING.
+	 *
+	 * The following task_is_stopped() test is safe as both transitions
+	 * in and out of STOPPED are protected by siglock.
+	 */
+	if (task_is_stopped(task)) {
+		task->group_stop |= GROUP_STOP_PENDING | GROUP_STOP_TRAPPING;
+		signal_wake_up(task, 1);
+		wait_trap = true;
+	}
+
+	spin_unlock(&task->sighand->siglock);
+
 	retval = 0;
 unlock_tasklist:
 	write_unlock_irq(&tasklist_lock);
 unlock_creds:
 	mutex_unlock(&task->signal->cred_guard_mutex);
 out:
+	if (wait_trap)
+		wait_event(current->signal->wait_chldexit,
+			   !(task->group_stop & GROUP_STOP_TRAPPING));
 	return retval;
 }
 
@@ -316,8 +362,6 @@ static int ptrace_detach(struct task_struct *child, unsigned int data)
 	if (child->ptrace) {
 		child->exit_code = data;
 		dead = __ptrace_detach(current, child);
-		if (!child->exit_state)
-			wake_up_state(child, TASK_TRACED | TASK_STOPPED);
 	}
 	write_unlock_irq(&tasklist_lock);
 
diff --git a/kernel/signal.c b/kernel/signal.c
index 7165af5f1b1..ad5e818baac 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -124,7 +124,7 @@ static inline int has_pending_signals(sigset_t *signal, sigset_t *blocked)
 
 static int recalc_sigpending_tsk(struct task_struct *t)
 {
-	if (t->signal->group_stop_count > 0 ||
+	if ((t->group_stop & GROUP_STOP_PENDING) ||
 	    PENDING(&t->pending, &t->blocked) ||
 	    PENDING(&t->signal->shared_pending, &t->blocked)) {
 		set_tsk_thread_flag(t, TIF_SIGPENDING);
@@ -223,6 +223,83 @@ static inline void print_dropped_signal(int sig)
 				current->comm, current->pid, sig);
 }
 
+/**
+ * task_clear_group_stop_trapping - clear group stop trapping bit
+ * @task: target task
+ *
+ * If GROUP_STOP_TRAPPING is set, a ptracer is waiting for us.  Clear it
+ * and wake up the ptracer.  Note that we don't need any further locking.
+ * @task->siglock guarantees that @task->parent points to the ptracer.
+ *
+ * CONTEXT:
+ * Must be called with @task->sighand->siglock held.
+ */
+static void task_clear_group_stop_trapping(struct task_struct *task)
+{
+	if (unlikely(task->group_stop & GROUP_STOP_TRAPPING)) {
+		task->group_stop &= ~GROUP_STOP_TRAPPING;
+		__wake_up_sync_key(&task->parent->signal->wait_chldexit,
+				   TASK_UNINTERRUPTIBLE, 1, task);
+	}
+}
+
+/**
+ * task_clear_group_stop_pending - clear pending group stop
+ * @task: target task
+ *
+ * Clear group stop states for @task.
+ *
+ * CONTEXT:
+ * Must be called with @task->sighand->siglock held.
+ */
+void task_clear_group_stop_pending(struct task_struct *task)
+{
+	task->group_stop &= ~(GROUP_STOP_PENDING | GROUP_STOP_CONSUME |
+			      GROUP_STOP_DEQUEUED);
+}
+
+/**
+ * task_participate_group_stop - participate in a group stop
+ * @task: task participating in a group stop
+ *
+ * @task has GROUP_STOP_PENDING set and is participating in a group stop.
+ * Group stop states are cleared and the group stop count is consumed if
+ * %GROUP_STOP_CONSUME was set.  If the consumption completes the group
+ * stop, the appropriate %SIGNAL_* flags are set.
+ *
+ * CONTEXT:
+ * Must be called with @task->sighand->siglock held.
+ *
+ * RETURNS:
+ * %true if group stop completion should be notified to the parent, %false
+ * otherwise.
+ */
+static bool task_participate_group_stop(struct task_struct *task)
+{
+	struct signal_struct *sig = task->signal;
+	bool consume = task->group_stop & GROUP_STOP_CONSUME;
+
+	WARN_ON_ONCE(!(task->group_stop & GROUP_STOP_PENDING));
+
+	task_clear_group_stop_pending(task);
+
+	if (!consume)
+		return false;
+
+	if (!WARN_ON_ONCE(sig->group_stop_count == 0))
+		sig->group_stop_count--;
+
+	/*
+	 * Tell the caller to notify completion iff we are entering into a
+	 * fresh group stop.  Read comment in do_signal_stop() for details.
+	 */
+	if (!sig->group_stop_count && !(sig->flags & SIGNAL_STOP_STOPPED)) {
+		sig->flags = SIGNAL_STOP_STOPPED;
+		return true;
+	}
+	return false;
+}
+
 /*
  * allocate a new signal queue record
  * - this may be called without locks if and only if t == current, otherwise an
@@ -527,7 +604,7 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info)
 		 * is to alert stop-signal processing code when another
 		 * processor has come along and cleared the flag.
 		 */
-		tsk->signal->flags |= SIGNAL_STOP_DEQUEUED;
+		current->group_stop |= GROUP_STOP_DEQUEUED;
 	}
 	if ((info->si_code & __SI_MASK) == __SI_TIMER && info->si_sys_private) {
 		/*
@@ -592,7 +669,7 @@ static int rm_from_queue_full(sigset_t *mask, struct sigpending *s)
 	if (sigisemptyset(&m))
 		return 0;
 
-	signandsets(&s->signal, &s->signal, mask);
+	sigandnsets(&s->signal, &s->signal, mask);
 	list_for_each_entry_safe(q, n, &s->list, list) {
 		if (sigismember(mask, q->info.si_signo)) {
 			list_del_init(&q->list);
@@ -727,34 +804,14 @@ static int prepare_signal(int sig, struct task_struct *p, int from_ancestor_ns)
 	} else if (sig == SIGCONT) {
 		unsigned int why;
 		/*
-		 * Remove all stop signals from all queues,
-		 * and wake all threads.
+		 * Remove all stop signals from all queues, wake all threads.
 		 */
 		rm_from_queue(SIG_KERNEL_STOP_MASK, &signal->shared_pending);
 		t = p;
 		do {
-			unsigned int state;
+			task_clear_group_stop_pending(t);
 			rm_from_queue(SIG_KERNEL_STOP_MASK, &t->pending);
-			/*
-			 * If there is a handler for SIGCONT, we must make
-			 * sure that no thread returns to user mode before
-			 * we post the signal, in case it was the only
-			 * thread eligible to run the signal handler--then
-			 * it must not do anything between resuming and
-			 * running the handler.  With the TIF_SIGPENDING
-			 * flag set, the thread will pause and acquire the
-			 * siglock that we hold now and until we've queued
-			 * the pending signal.
-			 *
-			 * Wake up the stopped thread _after_ setting
-			 * TIF_SIGPENDING
-			 */
-			state = __TASK_STOPPED;
-			if (sig_user_defined(t, SIGCONT) && !sigismember(&t->blocked, SIGCONT)) {
-				set_tsk_thread_flag(t, TIF_SIGPENDING);
-				state |= TASK_INTERRUPTIBLE;
-			}
-			wake_up_state(t, state);
+			wake_up_state(t, __TASK_STOPPED);
 		} while_each_thread(p, t);
 
 		/*
@@ -780,13 +837,6 @@ static int prepare_signal(int sig, struct task_struct *p, int from_ancestor_ns)
 			signal->flags = why | SIGNAL_STOP_CONTINUED;
 			signal->group_stop_count = 0;
 			signal->group_exit_code = 0;
-		} else {
-			/*
-			 * We are not stopped, but there could be a stop
-			 * signal in the middle of being processed after
-			 * being removed from the queue.  Clear that too.
-			 */
-			signal->flags &= ~SIGNAL_STOP_DEQUEUED;
 		}
 	}
 
@@ -875,6 +925,7 @@ static void complete_signal(int sig, struct task_struct *p, int group)
 			signal->group_stop_count = 0;
 			t = p;
 			do {
+				task_clear_group_stop_pending(t);
 				sigaddset(&t->pending.signal, SIGKILL);
 				signal_wake_up(t, 1);
 			} while_each_thread(p, t);
@@ -1109,6 +1160,7 @@ int zap_other_threads(struct task_struct *p)
 	p->signal->group_stop_count = 0;
 
 	while_each_thread(p, t) {
+		task_clear_group_stop_pending(t);
 		count++;
 
 		/* Don't bother with already dead threads */
@@ -1536,16 +1588,30 @@ int do_notify_parent(struct task_struct *tsk, int sig)
 	return ret;
 }
 
-static void do_notify_parent_cldstop(struct task_struct *tsk, int why)
+/**
+ * do_notify_parent_cldstop - notify parent of stopped/continued state change
+ * @tsk: task reporting the state change
+ * @for_ptracer: the notification is for ptracer
+ * @why: CLD_{CONTINUED|STOPPED|TRAPPED} to report
+ *
+ * Notify @tsk's parent that the stopped/continued state has changed.  If
+ * @for_ptracer is %false, @tsk's group leader notifies to its real parent.
+ * If %true, @tsk reports to @tsk->parent which should be the ptracer.
+ *
+ * CONTEXT:
+ * Must be called with tasklist_lock at least read locked.
+ */
+static void do_notify_parent_cldstop(struct task_struct *tsk,
+				     bool for_ptracer, int why)
 {
 	struct siginfo info;
 	unsigned long flags;
 	struct task_struct *parent;
 	struct sighand_struct *sighand;
 
-	if (task_ptrace(tsk))
+	if (for_ptracer) {
 		parent = tsk->parent;
-	else {
+	} else {
 		tsk = tsk->group_leader;
 		parent = tsk->real_parent;
 	}
@@ -1621,6 +1687,15 @@ static int sigkill_pending(struct task_struct *tsk)
 }
 
 /*
+ * Test whether the target task of the usual cldstop notification - the
+ * real_parent of @child - is in the same group as the ptracer.
+ */
+static bool real_parent_is_ptracer(struct task_struct *child)
+{
+	return same_thread_group(child->parent, child->real_parent);
+}
+
+/*
  * This must be called with current->sighand->siglock held.
  *
  * This should be the path for all ptrace stops.
@@ -1631,10 +1706,12 @@ static int sigkill_pending(struct task_struct *tsk)
  * If we actually decide not to stop at all because the tracer
  * is gone, we keep current->exit_code unless clear_code.
  */
-static void ptrace_stop(int exit_code, int clear_code, siginfo_t *info)
+static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info)
 	__releases(&current->sighand->siglock)
 	__acquires(&current->sighand->siglock)
 {
+	bool gstop_done = false;
+
 	if (arch_ptrace_stop_needed(exit_code, info)) {
 		/*
 		 * The arch code has something special to do before a
@@ -1655,21 +1732,49 @@ static void ptrace_stop(int exit_code, int clear_code, siginfo_t *info)
 	}
 
 	/*
-	 * If there is a group stop in progress,
-	 * we must participate in the bookkeeping.
+	 * If @why is CLD_STOPPED, we're trapping to participate in a group
+	 * stop.  Do the bookkeeping.  Note that if SIGCONT was delievered
+	 * while siglock was released for the arch hook, PENDING could be
+	 * clear now.  We act as if SIGCONT is received after TASK_TRACED
+	 * is entered - ignore it.
 	 */
-	if (current->signal->group_stop_count > 0)
-		--current->signal->group_stop_count;
+	if (why == CLD_STOPPED && (current->group_stop & GROUP_STOP_PENDING))
+		gstop_done = task_participate_group_stop(current);
 
 	current->last_siginfo = info;
 	current->exit_code = exit_code;
 
-	/* Let the debugger run.  */
-	__set_current_state(TASK_TRACED);
+	/*
+	 * TRACED should be visible before TRAPPING is cleared; otherwise,
+	 * the tracer might fail do_wait().
+	 */
+	set_current_state(TASK_TRACED);
+
+	/*
+	 * We're committing to trapping.  Clearing GROUP_STOP_TRAPPING and
+	 * transition to TASK_TRACED should be atomic with respect to
+	 * siglock.  This hsould be done after the arch hook as siglock is
+	 * released and regrabbed across it.
+	 */
+	task_clear_group_stop_trapping(current);
+
 	spin_unlock_irq(&current->sighand->siglock);
 	read_lock(&tasklist_lock);
 	if (may_ptrace_stop()) {
-		do_notify_parent_cldstop(current, CLD_TRAPPED);
+		/*
+		 * Notify parents of the stop.
+		 *
+		 * While ptraced, there are two parents - the ptracer and
+		 * the real_parent of the group_leader.  The ptracer should
+		 * know about every stop while the real parent is only
+		 * interested in the completion of group stop.  The states
+		 * for the two don't interact with each other.  Notify
+		 * separately unless they're gonna be duplicates.
+		 */
+		do_notify_parent_cldstop(current, true, why);
+		if (gstop_done && !real_parent_is_ptracer(current))
+			do_notify_parent_cldstop(current, false, why);
+
 		/*
 		 * Don't want to allow preemption here, because
 		 * sys_ptrace() needs this task to be inactive.
@@ -1684,7 +1789,16 @@ static void ptrace_stop(int exit_code, int clear_code, siginfo_t *info)
 		/*
 		 * By the time we got the lock, our tracer went away.
 		 * Don't drop the lock yet, another tracer may come.
+		 *
+		 * If @gstop_done, the ptracer went away between group stop
+		 * completion and here.  During detach, it would have set
+		 * GROUP_STOP_PENDING on us and we'll re-enter TASK_STOPPED
+		 * in do_signal_stop() on return, so notifying the real
+		 * parent of the group stop completion is enough.
 		 */
+		if (gstop_done)
+			do_notify_parent_cldstop(current, false, why);
+
 		__set_current_state(TASK_RUNNING);
 		if (clear_code)
 			current->exit_code = 0;
@@ -1728,7 +1842,7 @@ void ptrace_notify(int exit_code)
 
 	/* Let the debugger run.  */
 	spin_lock_irq(&current->sighand->siglock);
-	ptrace_stop(exit_code, 1, &info);
+	ptrace_stop(exit_code, CLD_TRAPPED, 1, &info);
 	spin_unlock_irq(&current->sighand->siglock);
 }
 
@@ -1741,66 +1855,115 @@ void ptrace_notify(int exit_code)
 static int do_signal_stop(int signr)
 {
 	struct signal_struct *sig = current->signal;
-	int notify;
 
-	if (!sig->group_stop_count) {
+	if (!(current->group_stop & GROUP_STOP_PENDING)) {
+		unsigned int gstop = GROUP_STOP_PENDING | GROUP_STOP_CONSUME;
 		struct task_struct *t;
 
-		if (!likely(sig->flags & SIGNAL_STOP_DEQUEUED) ||
+		/* signr will be recorded in task->group_stop for retries */
+		WARN_ON_ONCE(signr & ~GROUP_STOP_SIGMASK);
+
+		if (!likely(current->group_stop & GROUP_STOP_DEQUEUED) ||
 		    unlikely(signal_group_exit(sig)))
 			return 0;
 		/*
-		 * There is no group stop already in progress.
-		 * We must initiate one now.
+		 * There is no group stop already in progress.  We must
+		 * initiate one now.
+		 *
+		 * While ptraced, a task may be resumed while group stop is
+		 * still in effect and then receive a stop signal and
+		 * initiate another group stop.  This deviates from the
+		 * usual behavior as two consecutive stop signals can't
+		 * cause two group stops when !ptraced.  That is why we
+		 * also check !task_is_stopped(t) below.
+		 *
+		 * The condition can be distinguished by testing whether
+		 * SIGNAL_STOP_STOPPED is already set.  Don't generate
+		 * group_exit_code in such case.
+		 *
+		 * This is not necessary for SIGNAL_STOP_CONTINUED because
+		 * an intervening stop signal is required to cause two
+		 * continued events regardless of ptrace.
 		 */
-		sig->group_exit_code = signr;
+		if (!(sig->flags & SIGNAL_STOP_STOPPED))
+			sig->group_exit_code = signr;
+		else
+			WARN_ON_ONCE(!task_ptrace(current));
 
+		current->group_stop &= ~GROUP_STOP_SIGMASK;
+		current->group_stop |= signr | gstop;
 		sig->group_stop_count = 1;
-		for (t = next_thread(current); t != current; t = next_thread(t))
+		for (t = next_thread(current); t != current;
+		     t = next_thread(t)) {
+			t->group_stop &= ~GROUP_STOP_SIGMASK;
 			/*
 			 * Setting state to TASK_STOPPED for a group
 			 * stop is always done with the siglock held,
 			 * so this check has no races.
 			 */
-			if (!(t->flags & PF_EXITING) &&
-			    !task_is_stopped_or_traced(t)) {
+			if (!(t->flags & PF_EXITING) && !task_is_stopped(t)) {
+				t->group_stop |= signr | gstop;
 				sig->group_stop_count++;
 				signal_wake_up(t, 0);
 			}
+		}
 	}
-	/*
-	 * If there are no other threads in the group, or if there is
-	 * a group stop in progress and we are the last to stop, report
-	 * to the parent.  When ptraced, every thread reports itself.
-	 */
-	notify = sig->group_stop_count == 1 ? CLD_STOPPED : 0;
-	notify = tracehook_notify_jctl(notify, CLD_STOPPED);
-	/*
-	 * tracehook_notify_jctl() can drop and reacquire siglock, so
-	 * we keep ->group_stop_count != 0 before the call. If SIGCONT
-	 * or SIGKILL comes in between ->group_stop_count == 0.
-	 */
-	if (sig->group_stop_count) {
-		if (!--sig->group_stop_count)
-			sig->flags = SIGNAL_STOP_STOPPED;
-		current->exit_code = sig->group_exit_code;
+retry:
+	if (likely(!task_ptrace(current))) {
+		int notify = 0;
+
+		/*
+		 * If there are no other threads in the group, or if there
+		 * is a group stop in progress and we are the last to stop,
+		 * report to the parent.
+		 */
+		if (task_participate_group_stop(current))
+			notify = CLD_STOPPED;
+
 		__set_current_state(TASK_STOPPED);
+		spin_unlock_irq(&current->sighand->siglock);
+
+		/*
+		 * Notify the parent of the group stop completion.  Because
+		 * we're not holding either the siglock or tasklist_lock
+		 * here, ptracer may attach inbetween; however, this is for
+		 * group stop and should always be delivered to the real
+		 * parent of the group leader.  The new ptracer will get
+		 * its notification when this task transitions into
+		 * TASK_TRACED.
+		 */
+		if (notify) {
+			read_lock(&tasklist_lock);
+			do_notify_parent_cldstop(current, false, notify);
+			read_unlock(&tasklist_lock);
+		}
+
+		/* Now we don't run again until woken by SIGCONT or SIGKILL */
+		schedule();
+
+		spin_lock_irq(&current->sighand->siglock);
+	} else {
+		ptrace_stop(current->group_stop & GROUP_STOP_SIGMASK,
+			    CLD_STOPPED, 0, NULL);
+		current->exit_code = 0;
 	}
-	spin_unlock_irq(&current->sighand->siglock);
 
-	if (notify) {
-		read_lock(&tasklist_lock);
-		do_notify_parent_cldstop(current, notify);
-		read_unlock(&tasklist_lock);
+	/*
+	 * GROUP_STOP_PENDING could be set if another group stop has
+	 * started since being woken up or ptrace wants us to transit
+	 * between TASK_STOPPED and TRACED.  Retry group stop.
+	 */
+	if (current->group_stop & GROUP_STOP_PENDING) {
+		WARN_ON_ONCE(!(current->group_stop & GROUP_STOP_SIGMASK));
+		goto retry;
 	}
 
-	/* Now we don't run again until woken by SIGCONT or SIGKILL */
-	do {
-		schedule();
-	} while (try_to_freeze());
+	/* PTRACE_ATTACH might have raced with task killing, clear trapping */
+	task_clear_group_stop_trapping(current);
+
+	spin_unlock_irq(&current->sighand->siglock);
 
 	tracehook_finish_jctl();
-	current->exit_code = 0;
 
 	return 1;
 }
@@ -1814,7 +1977,7 @@ static int ptrace_signal(int signr, siginfo_t *info,
 	ptrace_signal_deliver(regs, cookie);
 
 	/* Let the debugger run.  */
-	ptrace_stop(signr, 0, info);
+	ptrace_stop(signr, CLD_TRAPPED, 0, info);
 
 	/* We're back.  Did the debugger cancel the sig?  */
 	signr = current->exit_code;
@@ -1869,18 +2032,36 @@ relock:
 	 * the CLD_ si_code into SIGNAL_CLD_MASK bits.
 	 */
 	if (unlikely(signal->flags & SIGNAL_CLD_MASK)) {
-		int why = (signal->flags & SIGNAL_STOP_CONTINUED)
-				? CLD_CONTINUED : CLD_STOPPED;
+		struct task_struct *leader;
+		int why;
+
+		if (signal->flags & SIGNAL_CLD_CONTINUED)
+			why = CLD_CONTINUED;
+		else
+			why = CLD_STOPPED;
+
 		signal->flags &= ~SIGNAL_CLD_MASK;
 
-		why = tracehook_notify_jctl(why, CLD_CONTINUED);
 		spin_unlock_irq(&sighand->siglock);
 
-		if (why) {
-			read_lock(&tasklist_lock);
-			do_notify_parent_cldstop(current->group_leader, why);
-			read_unlock(&tasklist_lock);
-		}
+		/*
+		 * Notify the parent that we're continuing.  This event is
+		 * always per-process and doesn't make whole lot of sense
+		 * for ptracers, who shouldn't consume the state via
+		 * wait(2) either, but, for backward compatibility, notify
+		 * the ptracer of the group leader too unless it's gonna be
+		 * a duplicate.
+		 */
+		read_lock(&tasklist_lock);
+
+		do_notify_parent_cldstop(current, false, why);
+
+		leader = current->group_leader;
+		if (task_ptrace(leader) && !real_parent_is_ptracer(leader))
+			do_notify_parent_cldstop(leader, true, why);
+
+		read_unlock(&tasklist_lock);
+
 		goto relock;
 	}
 
@@ -1897,8 +2078,8 @@ relock:
 		if (unlikely(signr != 0))
 			ka = return_ka;
 		else {
-			if (unlikely(signal->group_stop_count > 0) &&
-			    do_signal_stop(0))
+			if (unlikely(current->group_stop &
+				     GROUP_STOP_PENDING) && do_signal_stop(0))
 				goto relock;
 
 			signr = dequeue_signal(current, &current->blocked,
@@ -2017,10 +2198,42 @@ relock:
 	return signr;
 }
 
+/*
+ * It could be that complete_signal() picked us to notify about the
+ * group-wide signal. Other threads should be notified now to take
+ * the shared signals in @which since we will not.
+ */
+static void retarget_shared_pending(struct task_struct *tsk, sigset_t *which)
+{
+	sigset_t retarget;
+	struct task_struct *t;
+
+	sigandsets(&retarget, &tsk->signal->shared_pending.signal, which);
+	if (sigisemptyset(&retarget))
+		return;
+
+	t = tsk;
+	while_each_thread(tsk, t) {
+		if (t->flags & PF_EXITING)
+			continue;
+
+		if (!has_pending_signals(&retarget, &t->blocked))
+			continue;
+		/* Remove the signals this thread can handle. */
+		sigandsets(&retarget, &retarget, &t->blocked);
+
+		if (!signal_pending(t))
+			signal_wake_up(t, 0);
+
+		if (sigisemptyset(&retarget))
+			break;
+	}
+}
+
 void exit_signals(struct task_struct *tsk)
 {
 	int group_stop = 0;
-	struct task_struct *t;
+	sigset_t unblocked;
 
 	if (thread_group_empty(tsk) || signal_group_exit(tsk->signal)) {
 		tsk->flags |= PF_EXITING;
@@ -2036,26 +2249,23 @@ void exit_signals(struct task_struct *tsk)
 	if (!signal_pending(tsk))
 		goto out;
 
-	/*
-	 * It could be that __group_complete_signal() choose us to
-	 * notify about group-wide signal. Another thread should be
-	 * woken now to take the signal since we will not.
-	 */
-	for (t = tsk; (t = next_thread(t)) != tsk; )
-		if (!signal_pending(t) && !(t->flags & PF_EXITING))
-			recalc_sigpending_and_wake(t);
+	unblocked = tsk->blocked;
+	signotset(&unblocked);
+	retarget_shared_pending(tsk, &unblocked);
 
-	if (unlikely(tsk->signal->group_stop_count) &&
-			!--tsk->signal->group_stop_count) {
-		tsk->signal->flags = SIGNAL_STOP_STOPPED;
-		group_stop = tracehook_notify_jctl(CLD_STOPPED, CLD_STOPPED);
-	}
+	if (unlikely(tsk->group_stop & GROUP_STOP_PENDING) &&
+	    task_participate_group_stop(tsk))
+		group_stop = CLD_STOPPED;
 out:
 	spin_unlock_irq(&tsk->sighand->siglock);
 
+	/*
+	 * If group stop has completed, deliver the notification.  This
+	 * should always go to the real parent of the group leader.
+	 */
 	if (unlikely(group_stop)) {
 		read_lock(&tasklist_lock);
-		do_notify_parent_cldstop(tsk, group_stop);
+		do_notify_parent_cldstop(tsk, false, group_stop);
 		read_unlock(&tasklist_lock);
 	}
 }
@@ -2089,11 +2299,33 @@ long do_no_restart_syscall(struct restart_block *param)
 	return -EINTR;
 }
 
-/*
- * We don't need to get the kernel lock - this is all local to this
- * particular thread.. (and that's good, because this is _heavily_
- * used by various programs)
+static void __set_task_blocked(struct task_struct *tsk, const sigset_t *newset)
+{
+	if (signal_pending(tsk) && !thread_group_empty(tsk)) {
+		sigset_t newblocked;
+		/* A set of now blocked but previously unblocked signals. */
+		sigandnsets(&newblocked, newset, &current->blocked);
+		retarget_shared_pending(tsk, &newblocked);
+	}
+	tsk->blocked = *newset;
+	recalc_sigpending();
+}
+
+/**
+ * set_current_blocked - change current->blocked mask
+ * @newset: new mask
+ *
+ * It is wrong to change ->blocked directly, this helper should be used
+ * to ensure the process can't miss a shared signal we are going to block.
  */
+void set_current_blocked(const sigset_t *newset)
+{
+	struct task_struct *tsk = current;
+
+	spin_lock_irq(&tsk->sighand->siglock);
+	__set_task_blocked(tsk, newset);
+	spin_unlock_irq(&tsk->sighand->siglock);
+}
 
 /*
  * This is also useful for kernel threads that want to temporarily
@@ -2105,30 +2337,29 @@ long do_no_restart_syscall(struct restart_block *param)
  */
 int sigprocmask(int how, sigset_t *set, sigset_t *oldset)
 {
-	int error;
+	struct task_struct *tsk = current;
+	sigset_t newset;
 
-	spin_lock_irq(&current->sighand->siglock);
+	/* Lockless, only current can change ->blocked, never from irq */
 	if (oldset)
-		*oldset = current->blocked;
+		*oldset = tsk->blocked;
 
-	error = 0;
 	switch (how) {
 	case SIG_BLOCK:
-		sigorsets(&current->blocked, &current->blocked, set);
+		sigorsets(&newset, &tsk->blocked, set);
 		break;
 	case SIG_UNBLOCK:
-		signandsets(&current->blocked, &current->blocked, set);
+		sigandnsets(&newset, &tsk->blocked, set);
 		break;
 	case SIG_SETMASK:
-		current->blocked = *set;
+		newset = *set;
 		break;
 	default:
-		error = -EINVAL;
+		return -EINVAL;
 	}
-	recalc_sigpending();
-	spin_unlock_irq(&current->sighand->siglock);
 
-	return error;
+	set_current_blocked(&newset);
+	return 0;
 }
 
 /**
@@ -2138,40 +2369,34 @@ int sigprocmask(int how, sigset_t *set, sigset_t *oldset)
  *  @oset: previous value of signal mask if non-null
  *  @sigsetsize: size of sigset_t type
  */
-SYSCALL_DEFINE4(rt_sigprocmask, int, how, sigset_t __user *, set,
+SYSCALL_DEFINE4(rt_sigprocmask, int, how, sigset_t __user *, nset,
 		sigset_t __user *, oset, size_t, sigsetsize)
 {
-	int error = -EINVAL;
 	sigset_t old_set, new_set;
+	int error;
 
 	/* XXX: Don't preclude handling different sized sigset_t's.  */
 	if (sigsetsize != sizeof(sigset_t))
-		goto out;
+		return -EINVAL;
 
-	if (set) {
-		error = -EFAULT;
-		if (copy_from_user(&new_set, set, sizeof(*set)))
-			goto out;
+	old_set = current->blocked;
+
+	if (nset) {
+		if (copy_from_user(&new_set, nset, sizeof(sigset_t)))
+			return -EFAULT;
 		sigdelsetmask(&new_set, sigmask(SIGKILL)|sigmask(SIGSTOP));
 
-		error = sigprocmask(how, &new_set, &old_set);
+		error = sigprocmask(how, &new_set, NULL);
 		if (error)
-			goto out;
-		if (oset)
-			goto set_old;
-	} else if (oset) {
-		spin_lock_irq(&current->sighand->siglock);
-		old_set = current->blocked;
-		spin_unlock_irq(&current->sighand->siglock);
+			return error;
+	}
 
-	set_old:
-		error = -EFAULT;
-		if (copy_to_user(oset, &old_set, sizeof(*oset)))
-			goto out;
+	if (oset) {
+		if (copy_to_user(oset, &old_set, sizeof(sigset_t)))
+			return -EFAULT;
 	}
-	error = 0;
-out:
-	return error;
+
+	return 0;
 }
 
 long do_sigpending(void __user *set, unsigned long sigsetsize)
@@ -2284,6 +2509,66 @@ int copy_siginfo_to_user(siginfo_t __user *to, siginfo_t *from)
 #endif
 
 /**
+ *  do_sigtimedwait - wait for queued signals specified in @which
+ *  @which: queued signals to wait for
+ *  @info: if non-null, the signal's siginfo is returned here
+ *  @ts: upper bound on process time suspension
+ */
+int do_sigtimedwait(const sigset_t *which, siginfo_t *info,
+			const struct timespec *ts)
+{
+	struct task_struct *tsk = current;
+	long timeout = MAX_SCHEDULE_TIMEOUT;
+	sigset_t mask = *which;
+	int sig;
+
+	if (ts) {
+		if (!timespec_valid(ts))
+			return -EINVAL;
+		timeout = timespec_to_jiffies(ts);
+		/*
+		 * We can be close to the next tick, add another one
+		 * to ensure we will wait at least the time asked for.
+		 */
+		if (ts->tv_sec || ts->tv_nsec)
+			timeout++;
+	}
+
+	/*
+	 * Invert the set of allowed signals to get those we want to block.
+	 */
+	sigdelsetmask(&mask, sigmask(SIGKILL) | sigmask(SIGSTOP));
+	signotset(&mask);
+
+	spin_lock_irq(&tsk->sighand->siglock);
+	sig = dequeue_signal(tsk, &mask, info);
+	if (!sig && timeout) {
+		/*
+		 * None ready, temporarily unblock those we're interested
+		 * while we are sleeping in so that we'll be awakened when
+		 * they arrive. Unblocking is always fine, we can avoid
+		 * set_current_blocked().
+		 */
+		tsk->real_blocked = tsk->blocked;
+		sigandsets(&tsk->blocked, &tsk->blocked, &mask);
+		recalc_sigpending();
+		spin_unlock_irq(&tsk->sighand->siglock);
+
+		timeout = schedule_timeout_interruptible(timeout);
+
+		spin_lock_irq(&tsk->sighand->siglock);
+		__set_task_blocked(tsk, &tsk->real_blocked);
+		siginitset(&tsk->real_blocked, 0);
+		sig = dequeue_signal(tsk, &mask, info);
+	}
+	spin_unlock_irq(&tsk->sighand->siglock);
+
+	if (sig)
+		return sig;
+	return timeout ? -EINTR : -EAGAIN;
+}
+
+/**
  *  sys_rt_sigtimedwait - synchronously wait for queued signals specified
  *			in @uthese
  *  @uthese: queued signals to wait for
@@ -2295,11 +2580,10 @@ SYSCALL_DEFINE4(rt_sigtimedwait, const sigset_t __user *, uthese,
 		siginfo_t __user *, uinfo, const struct timespec __user *, uts,
 		size_t, sigsetsize)
 {
-	int ret, sig;
 	sigset_t these;
 	struct timespec ts;
 	siginfo_t info;
-	long timeout = 0;
+	int ret;
 
 	/* XXX: Don't preclude handling different sized sigset_t's.  */
 	if (sigsetsize != sizeof(sigset_t))
@@ -2308,61 +2592,16 @@ SYSCALL_DEFINE4(rt_sigtimedwait, const sigset_t __user *, uthese,
 	if (copy_from_user(&these, uthese, sizeof(these)))
 		return -EFAULT;
 
-	/*
-	 * Invert the set of allowed signals to get those we
-	 * want to block.
-	 */
-	sigdelsetmask(&these, sigmask(SIGKILL)|sigmask(SIGSTOP));
-	signotset(&these);
-
 	if (uts) {
 		if (copy_from_user(&ts, uts, sizeof(ts)))
 			return -EFAULT;
-		if (ts.tv_nsec >= 1000000000L || ts.tv_nsec < 0
-		    || ts.tv_sec < 0)
-			return -EINVAL;
 	}
 
-	spin_lock_irq(&current->sighand->siglock);
-	sig = dequeue_signal(current, &these, &info);
-	if (!sig) {
-		timeout = MAX_SCHEDULE_TIMEOUT;
-		if (uts)
-			timeout = (timespec_to_jiffies(&ts)
-				   + (ts.tv_sec || ts.tv_nsec));
-
-		if (timeout) {
-			/*
-			 * None ready -- temporarily unblock those we're
-			 * interested while we are sleeping in so that we'll
-			 * be awakened when they arrive.
-			 */
-			current->real_blocked = current->blocked;
-			sigandsets(&current->blocked, &current->blocked, &these);
-			recalc_sigpending();
-			spin_unlock_irq(&current->sighand->siglock);
-
-			timeout = schedule_timeout_interruptible(timeout);
-
-			spin_lock_irq(&current->sighand->siglock);
-			sig = dequeue_signal(current, &these, &info);
-			current->blocked = current->real_blocked;
-			siginitset(&current->real_blocked, 0);
-			recalc_sigpending();
-		}
-	}
-	spin_unlock_irq(&current->sighand->siglock);
+	ret = do_sigtimedwait(&these, &info, uts ? &ts : NULL);
 
-	if (sig) {
-		ret = sig;
-		if (uinfo) {
-			if (copy_siginfo_to_user(uinfo, &info))
-				ret = -EFAULT;
-		}
-	} else {
-		ret = -EAGAIN;
-		if (timeout)
-			ret = -EINTR;
+	if (ret > 0 && uinfo) {
+		if (copy_siginfo_to_user(uinfo, &info))
+			ret = -EFAULT;
 	}
 
 	return ret;
@@ -2650,60 +2889,51 @@ SYSCALL_DEFINE1(sigpending, old_sigset_t __user *, set)
 /**
  *  sys_sigprocmask - examine and change blocked signals
  *  @how: whether to add, remove, or set signals
- *  @set: signals to add or remove (if non-null)
+ *  @nset: signals to add or remove (if non-null)
  *  @oset: previous value of signal mask if non-null
  *
  * Some platforms have their own version with special arguments;
  * others support only sys_rt_sigprocmask.
  */
 
-SYSCALL_DEFINE3(sigprocmask, int, how, old_sigset_t __user *, set,
+SYSCALL_DEFINE3(sigprocmask, int, how, old_sigset_t __user *, nset,
 		old_sigset_t __user *, oset)
 {
-	int error;
 	old_sigset_t old_set, new_set;
+	sigset_t new_blocked;
 
-	if (set) {
-		error = -EFAULT;
-		if (copy_from_user(&new_set, set, sizeof(*set)))
-			goto out;
+	old_set = current->blocked.sig[0];
+
+	if (nset) {
+		if (copy_from_user(&new_set, nset, sizeof(*nset)))
+			return -EFAULT;
 		new_set &= ~(sigmask(SIGKILL) | sigmask(SIGSTOP));
 
-		spin_lock_irq(&current->sighand->siglock);
-		old_set = current->blocked.sig[0];
+		new_blocked = current->blocked;
 
-		error = 0;
 		switch (how) {
-		default:
-			error = -EINVAL;
-			break;
 		case SIG_BLOCK:
-			sigaddsetmask(&current->blocked, new_set);
+			sigaddsetmask(&new_blocked, new_set);
 			break;
 		case SIG_UNBLOCK:
-			sigdelsetmask(&current->blocked, new_set);
+			sigdelsetmask(&new_blocked, new_set);
 			break;
 		case SIG_SETMASK:
-			current->blocked.sig[0] = new_set;
+			new_blocked.sig[0] = new_set;
 			break;
+		default:
+			return -EINVAL;
 		}
 
-		recalc_sigpending();
-		spin_unlock_irq(&current->sighand->siglock);
-		if (error)
-			goto out;
-		if (oset)
-			goto set_old;
-	} else if (oset) {
-		old_set = current->blocked.sig[0];
-	set_old:
-		error = -EFAULT;
+		set_current_blocked(&new_blocked);
+	}
+
+	if (oset) {
 		if (copy_to_user(oset, &old_set, sizeof(*oset)))
-			goto out;
+			return -EFAULT;
 	}
-	error = 0;
-out:
-	return error;
+
+	return 0;
 }
 #endif /* __ARCH_WANT_SYS_SIGPROCMASK */