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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).

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Jerome Marchand 2011-06-10 15:28:49 +02:00 committed by Greg Kroah-Hartman
parent 924bd88d70
commit c5bde2388e
2 changed files with 15 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
drivers/staging/zram/zram_drv.c
View File

@ -359,8 +359,6 @@ 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 (is_partial_io(bvec))
@ -371,7 +369,6 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
if (page_zero_filled(uncmem)) {
kunmap_atomic(user_mem, KM_USER0);
mutex_unlock(&zram->lock);
if (is_partial_io(bvec))
kfree(uncmem);
zram_stat_inc(&zram->stats.pages_zero);
@ -388,7 +385,6 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
kfree(uncmem);
if (unlikely(ret != LZO_E_OK)) {
mutex_unlock(&zram->lock);
pr_err("Compression failed! err=%d\n", ret);
goto out;
}
@ -402,7 +398,6 @@ 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);
ret = -ENOMEM;
@ -420,7 +415,6 @@ 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, &store_offset,
GFP_NOIO | __GFP_HIGHMEM)) {
mutex_unlock(&zram->lock);
pr_info("Error allocating memory for compressed "
"page: %u, size=%zu\n", index, clen);
ret = -ENOMEM;
@ -454,8 +448,6 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
if (clen <= PAGE_SIZE / 2)
zram_stat_inc(&zram->stats.good_compress);
mutex_unlock(&zram->lock);
return 0;
out:
@ -467,10 +459,19 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
int offset, struct bio *bio, int rw)
{
if (rw == READ)
return zram_bvec_read(zram, bvec, index, offset, bio);
int ret;
return zram_bvec_write(zram, bvec, index, offset);
if (rw == READ) {
down_read(&zram->lock);
ret = zram_bvec_read(zram, bvec, index, offset, bio);
up_read(&zram->lock);
} else {
down_write(&zram->lock);
ret = zram_bvec_write(zram, bvec, index, offset);
up_write(&zram->lock);
}
return ret;
}
static void update_position(u32 *index, int *offset, struct bio_vec *bvec)
@ -701,7 +702,7 @@ 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);

4
drivers/staging/zram/zram_drv.h
View File

@ -107,8 +107,8 @@ 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 and table
* against concurrent read and writes */
struct request_queue *queue;
struct gendisk *disk;
int init_done;