[PATCH 50/88] zram: Fix deadlock bug in partial read/write

[Luis Henriques]

3.5.7.8 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Minchan Kim <minchan at kernel.org>

commit 7e5a5104c6af709a8d97d5f4711e7c917761d464 upstream.

Now zram allocates new page with GFP_KERNEL in zram I/O path
if IO is partial. Unfortunately, It may cause deadlock with
reclaim path like below.

write_page from fs
fs_lock
allocation(GFP_KERNEL)
reclaim
pageout
				write_page from fs
				fs_lock <-- deadlock

This patch fixes it by using GFP_NOIO.  In read path, we
reorganize code flow so that kmap_atomic is called after the
GFP_NOIO allocation.

Acked-by: Jerome Marchand <jmarchand at redhat.com>
Acked-by: Nitin Gupta <ngupta at vflare.org>
[ penberg at kernel.org: don't use GFP_ATOMIC ]
Signed-off-by: Pekka Enberg <penberg at kernel.org>
Signed-off-by: Minchan Kim <minchan at kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/staging/zram/zram_drv.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index 685d612..fb7f9fb 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -235,7 +235,7 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 
 	if (is_partial_io(bvec)) {
 		/* Use  a temporary buffer to decompress the page */
-		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
+		uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
 		if (!uncmem) {
 			pr_info("Error allocating temp memory!\n");
 			return -ENOMEM;
@@ -330,7 +330,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 		 * This is a partial IO. We need to read the full page
 		 * before to write the changes.
 		 */
-		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
+		uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
 		if (!uncmem) {
 			pr_info("Error allocating temp memory!\n");
 			ret = -ENOMEM;
-- 
1.8.1.2