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authorJerome Marchand <jmarchan@redhat.com>2012-05-14 11:21:07 -0500
committerSimon Shields <keepcalm444@gmail.com>2016-06-12 21:19:24 +1000
commitf526a35a01423d3760e773604b763e8a7aeeb6c1 (patch)
tree0dd7f723b00b304d2c8746cf748886ea9c371f82 /drivers/staging
parentdc3b0f18a7172f56a5ba1375c3e2f15fed6a9b25 (diff)
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Staging: zram: Replace mutex lock by a R/W semaphore
Currently, nothing protects zram table from concurrent access. For instance, ZRAM_UNCOMPRESSED bit can be cleared by zram_free_page() called from a concurrent write between the time ZRAM_UNCOMPRESSED has been set and the time it is tested to unmap KM_USER0 in zram_bvec_write(). This ultimately leads to kernel panic. Also, a read request can occurs when the page has been freed by a running write request and before it has been updated, leading to zero filled block being incorrectly read and "Read before write" error message. This patch replace the current mutex by a rw_semaphore. It extends the protection to zram table (currently, only compression buffers are protected) and read requests (currently, only write requests are protected). Change-Id: Ie2b2608ff55dd655037b48a6f7370a819c9b581a Signed-off-by: Jerome Marchand <jmarchan@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> Signed-off-by: Jason Hrycay <jason.hrycay@motorola.com> Reviewed-on: http://gerrit.pcs.mot.com/414992 Tested-by: Jira Key <JIRAKEY@motorola.com> Reviewed-by: Christopher Fries <C.Fries@motorola.com> Reviewed-by: Neil Patel <NPATEL@motorola.com> Reviewed-by: David Ding <dding@motorola.com>
Diffstat (limited to 'drivers/staging')
-rw-r--r--drivers/staging/zram/zram_drv.c25
-rw-r--r--drivers/staging/zram/zram_drv.h4
2 files changed, 15 insertions, 14 deletions
diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index 9b311638120..2095478b2e7 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -279,12 +279,9 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index)
zram_test_flag(zram, index, ZRAM_ZERO))
zram_free_page(zram, index);
- mutex_lock(&zram->lock);
-
user_mem = kmap_atomic(page, KM_USER0);
if (page_zero_filled(user_mem)) {
kunmap_atomic(user_mem, KM_USER0);
- mutex_unlock(&zram->lock);
zram_stat_inc(&zram->stats.pages_zero);
zram_set_flag(zram, index, ZRAM_ZERO);
return 0;
@@ -296,7 +293,6 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index)
kunmap_atomic(user_mem, KM_USER0);
if (unlikely(ret != LZO_E_OK)) {
- mutex_unlock(&zram->lock);
pr_err("Compression failed! err=%d\n", ret);
zram_stat64_inc(zram, &zram->stats.failed_writes);
return ret;
@@ -311,7 +307,6 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index)
clen = PAGE_SIZE;
page_store = alloc_page(GFP_NOIO | __GFP_HIGHMEM);
if (unlikely(!page_store)) {
- mutex_unlock(&zram->lock);
pr_info("Error allocating memory for "
"incompressible page: %u\n", index);
zram_stat64_inc(zram, &zram->stats.failed_writes);
@@ -329,7 +324,6 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index)
if (xv_malloc(zram->mem_pool, clen + sizeof(*zheader),
&zram->table[index].page, &offset,
GFP_NOIO | __GFP_HIGHMEM)) {
- mutex_unlock(&zram->lock);
pr_info("Error allocating memory for compressed "
"page: %u, size=%zu\n", index, clen);
zram_stat64_inc(zram, &zram->stats.failed_writes);
@@ -363,18 +357,25 @@ memstore:
if (clen <= PAGE_SIZE / 2)
zram_stat_inc(&zram->stats.good_compress);
- mutex_unlock(&zram->lock);
-
return 0;
}
static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
struct bio *bio, int rw)
{
- if (rw == READ)
- return zram_bvec_read(zram, bvec, index, bio);
+ int ret;
- return zram_bvec_write(zram, bvec, index);
+ if (rw == READ) {
+ down_read(&zram->lock);
+ ret = zram_bvec_read(zram, bvec, index, bio);
+ up_read(&zram->lock);
+ } else {
+ down_write(&zram->lock);
+ ret = zram_bvec_write(zram, bvec, index);
+ up_write(&zram->lock);
+ }
+
+ return ret;
}
static void __zram_make_request(struct zram *zram, struct bio *bio, int rw)
@@ -574,7 +575,7 @@ static int create_device(struct zram *zram, int device_id)
{
int ret = 0;
- mutex_init(&zram->lock);
+ init_rwsem(&zram->lock);
mutex_init(&zram->init_lock);
spin_lock_init(&zram->stat64_lock);
diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h
index 408b2c067fc..1db8f19a093 100644
--- a/drivers/staging/zram/zram_drv.h
+++ b/drivers/staging/zram/zram_drv.h
@@ -104,8 +104,8 @@ struct zram {
void *compress_buffer;
struct table *table;
spinlock_t stat64_lock; /* protect 64-bit stats */
- struct mutex lock; /* protect compression buffers against
- * concurrent writes */
+ struct rw_semaphore lock; /* protect compression buffers against
+ * concurrent writes */
struct request_queue *queue;
struct gendisk *disk;
int init_done;