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authorH. Peter Anvin <hpa@zytor.com>2008-02-08 04:21:26 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-02-08 09:22:39 -0800
commitbdc807871d58285737d50dc6163d0feb72cb0dc2 (patch)
tree1a6d35f3537ed1a7460811549efd045ae97a0e6e /arch
parent7ef3d2fd17c377ef64a2aa19677d17576606c3b4 (diff)
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avoid overflows in kernel/time.c
When the conversion factor between jiffies and milli- or microseconds is not a single multiply or divide, as for the case of HZ == 300, we currently do a multiply followed by a divide. The intervening result, however, is subject to overflows, especially since the fraction is not simplified (for HZ == 300, we multiply by 300 and divide by 1000). This is exposed to the user when passing a large timeout to poll(), for example. This patch replaces the multiply-divide with a reciprocal multiplication on 32-bit platforms. When the input is an unsigned long, there is no portable way to do this on 64-bit platforms there is no portable way to do this since it requires a 128-bit intermediate result (which gcc does support on 64-bit platforms but may generate libgcc calls, e.g. on 64-bit s390), but since the output is a 32-bit integer in the cases affected, just simplify the multiply-divide (*3/10 instead of *300/1000). The reciprocal multiply used can have off-by-one errors in the upper half of the valid output range. This could be avoided at the expense of having to deal with a potential 65-bit intermediate result. Since the intent is to avoid overflow problems and most of the other time conversions are only semiexact, the off-by-one errors were considered an acceptable tradeoff. At Ralf Baechle's suggestion, this version uses a Perl script to compute the necessary constants. We already have dependencies on Perl for kernel compiles. This does, however, require the Perl module Math::BigInt, which is included in the standard Perl distribution starting with version 5.8.0. In order to support older versions of Perl, include a table of canned constants in the script itself, and structure the script so that Math::BigInt isn't required if pulling values from said table. Running the script requires that the HZ value is available from the Makefile. Thus, this patch also adds the Kconfig variable CONFIG_HZ to the architectures which didn't already have it (alpha, cris, frv, h8300, m32r, m68k, m68knommu, sparc, v850, and xtensa.) It does *not* touch the sh or sh64 architectures, since Paul Mundt has dealt with those separately in the sh tree. Signed-off-by: H. Peter Anvin <hpa@zytor.com> Cc: Ralf Baechle <ralf@linux-mips.org>, Cc: Sam Ravnborg <sam@ravnborg.org>, Cc: Paul Mundt <lethal@linux-sh.org>, Cc: Richard Henderson <rth@twiddle.net>, Cc: Michael Starvik <starvik@axis.com>, Cc: David Howells <dhowells@redhat.com>, Cc: Yoshinori Sato <ysato@users.sourceforge.jp>, Cc: Hirokazu Takata <takata@linux-m32r.org>, Cc: Geert Uytterhoeven <geert@linux-m68k.org>, Cc: Roman Zippel <zippel@linux-m68k.org>, Cc: William L. Irwin <sparclinux@vger.kernel.org>, Cc: Chris Zankel <chris@zankel.net>, Cc: H. Peter Anvin <hpa@zytor.com>, Cc: Jan Engelhardt <jengelh@computergmbh.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/alpha/Kconfig5
-rw-r--r--arch/cris/Kconfig4
-rw-r--r--arch/frv/Kconfig4
-rw-r--r--arch/h8300/Kconfig4
-rw-r--r--arch/m32r/Kconfig4
-rw-r--r--arch/m68k/Kconfig4
-rw-r--r--arch/m68knommu/Kconfig5
-rw-r--r--arch/sparc/Kconfig4
-rw-r--r--arch/v850/Kconfig7
-rw-r--r--arch/xtensa/Kconfig4
10 files changed, 45 insertions, 0 deletions
diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index d9df913a464..5b7dcd5a0e7 100644
--- a/arch/alpha/Kconfig
+++ b/arch/alpha/Kconfig
@@ -615,6 +615,11 @@ config VERBOSE_MCHECK_ON
Take the default (1) unless you want more control or more info.
+config HZ
+ int
+ default 1200 if ALPHA_RAWHIDE
+ default 1024
+
source "drivers/pci/Kconfig"
source "drivers/eisa/Kconfig"
diff --git a/arch/cris/Kconfig b/arch/cris/Kconfig
index 27b082ac7f1..ff078e60e76 100644
--- a/arch/cris/Kconfig
+++ b/arch/cris/Kconfig
@@ -55,6 +55,10 @@ config CRIS
bool
default y
+config HZ
+ int
+ default 100
+
source "init/Kconfig"
menu "General setup"
diff --git a/arch/frv/Kconfig b/arch/frv/Kconfig
index 96f7d70f447..9e561ede092 100644
--- a/arch/frv/Kconfig
+++ b/arch/frv/Kconfig
@@ -57,6 +57,10 @@ config ARCH_HAS_ILOG2_U64
bool
default y
+config HZ
+ int
+ default 1000
+
mainmenu "Fujitsu FR-V Kernel Configuration"
source "init/Kconfig"
diff --git a/arch/h8300/Kconfig b/arch/h8300/Kconfig
index b4ba4f8b505..f69e5ea3855 100644
--- a/arch/h8300/Kconfig
+++ b/arch/h8300/Kconfig
@@ -82,6 +82,10 @@ config PCI
bool
default n
+config HZ
+ int
+ default 100
+
source "init/Kconfig"
source "arch/h8300/Kconfig.cpu"
diff --git a/arch/m32r/Kconfig b/arch/m32r/Kconfig
index fe61e00a604..d4679ab55b9 100644
--- a/arch/m32r/Kconfig
+++ b/arch/m32r/Kconfig
@@ -38,6 +38,10 @@ config NO_DMA
config ARCH_SUPPORTS_AOUT
def_bool y
+config HZ
+ int
+ default 100
+
source "init/Kconfig"
diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
index bcbf3e4ee9d..2b0ed89cd17 100644
--- a/arch/m68k/Kconfig
+++ b/arch/m68k/Kconfig
@@ -55,6 +55,10 @@ config NO_DMA
config ARCH_SUPPORTS_AOUT
def_bool y
+config HZ
+ int
+ default 100
+
mainmenu "Linux/68k Kernel Configuration"
source "init/Kconfig"
diff --git a/arch/m68knommu/Kconfig b/arch/m68knommu/Kconfig
index 24f732342d3..548a7b32163 100644
--- a/arch/m68knommu/Kconfig
+++ b/arch/m68knommu/Kconfig
@@ -525,6 +525,11 @@ config 4KSTACKS
running more threads on a system and also reduces the pressure
on the VM subsystem for higher order allocations.
+config HZ
+ int
+ default 1000 if CLEOPATRA
+ default 100
+
comment "RAM configuration"
config RAMBASE
diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index 08821b078ec..7c674a3503b 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -30,6 +30,10 @@ config OF
config ARCH_SUPPORTS_AOUT
def_bool y
+config HZ
+ int
+ default 100
+
source "init/Kconfig"
menu "General machine setup"
diff --git a/arch/v850/Kconfig b/arch/v850/Kconfig
index 225f30d7cb3..7b6d3716efc 100644
--- a/arch/v850/Kconfig
+++ b/arch/v850/Kconfig
@@ -215,6 +215,13 @@ menu "Processor type and features"
bool
default !V850E_CACHE && !V850E2_CACHE
+ # HZ depends on the platform
+ config HZ
+ int
+ default 24 if V850E_SIM || V850E2_SIM85E2
+ default 122 if V850E2_FPGA85E2C
+ default 100
+
#### Misc config
config ROM_KERNEL
diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index 5d5546ce88f..fd36764d7fb 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -49,6 +49,10 @@ config ARCH_HAS_ILOG2_U64
config NO_IOPORT
def_bool y
+config HZ
+ int
+ default 100
+
source "init/Kconfig"
menu "Processor type and features"