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Message-Id: <1307712529-9757-4-git-send-email-jmarchan@redhat.com>
Date: Fri, 10 Jun 2011 15:28:49 +0200
From: Jerome Marchand <jmarchan@...hat.com>
To: Greg Kroah-Hartman <gregkh@...e.de>
Cc: Linux Kernel List <linux-kernel@...r.kernel.org>,
Nitin Gupta <ngupta@...are.org>,
Robert Jennings <rcj@...ux.vnet.ibm.com>,
Jeff Moyer <jmoyer@...hat.com>,
Jerome Marchand <jmarchan@...hat.com>
Subject: [PATCH 4/4] 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@...hat.com>
---
drivers/staging/zram/zram_drv.c | 25 +++++++++++++------------
drivers/staging/zram/zram_drv.h | 4 ++--
2 files changed, 15 insertions(+), 14 deletions(-)
diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index 54ad29d..c5fdc55 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -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 @@ memstore:
if (clen <= PAGE_SIZE / 2)
zram_stat_inc(&zram->stats.good_compress);
- mutex_unlock(&zram->lock);
-
return 0;
out:
@@ -467,10 +459,19 @@ out:
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);
diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h
index 8acf9eb..abe5221 100644
--- a/drivers/staging/zram/zram_drv.h
+++ b/drivers/staging/zram/zram_drv.h
@@ -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;
--
1.6.2.5
--
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