UPSTREAM: zram: avoid kunmap_atomic() of a NULL pointer

(cherry picked from commit c406515239376fc93a30d5d03192182160cbd3fb) zram could kunmap_atomic() a NULL pointer in a rare situation: a zram page becomes a full-zeroed page after a partial write io. The current code doesn't handle this case and performs kunmap_atomic() on a NULL pointer, which panics the kernel. This patch fixes this issue. Change-Id: I6358b55555328a97b1b9004629b87044c0e27fdd Signed-off-by: Weijie Yang <[email protected]> Cc: Sergey Senozhatsky <[email protected]> Cc: Dan Streetman <[email protected]> Cc: Nitin Gupta <[email protected]> Cc: Weijie Yang <[email protected]> Acked-by: Jerome Marchand <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> (cherry picked from commit ba922d3)
nasty007 · Dec 22, 2016 · 92107d5 · 92107d5
1 parent f616c4e
commit 92107d5
Showing 1 changed file with 2 additions and 1 deletion.
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
@@ -459,7 +459,8 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 	}
 
 	if (page_zero_filled(uncmem)) {
-		kunmap_atomic(user_mem);
+		if (user_mem)
+			kunmap_atomic(user_mem);
 		/* Free memory associated with this sector now. */
 		write_lock(&zram->meta->tb_lock);
 		zram_free_page(zram, index);