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>

1 files changed, 2 insertions, 2 deletions

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;