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authorJeff Moyer <jmoyer@redhat.com>2012-07-12 09:43:14 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2012-07-13 08:36:35 -0700
commit91f68c89d8f35fe98ea04159b9a3b42d0149478f (patch)
treed62ecd2a9de58a2d5673e4e1765b35eac28faf2c
parent918227bb1b59444a2c467711fd50cc22bb4a897b (diff)
block: fix infinite loop in __getblk_slow
Commit 080399aaaf35 ("block: don't mark buffers beyond end of disk as mapped") exposed a bug in __getblk_slow that causes mount to hang as it loops infinitely waiting for a buffer that lies beyond the end of the disk to become uptodate. The problem was initially reported by Torsten Hilbrich here: https://lkml.org/lkml/2012/6/18/54 and also reported independently here: http://www.sysresccd.org/forums/viewtopic.php?f=13&t=4511 and then Richard W.M. Jones and Marcos Mello noted a few separate bugzillas also associated with the same issue. This patch has been confirmed to fix: https://bugzilla.redhat.com/show_bug.cgi?id=835019 The main problem is here, in __getblk_slow: for (;;) { struct buffer_head * bh; int ret; bh = __find_get_block(bdev, block, size); if (bh) return bh; ret = grow_buffers(bdev, block, size); if (ret < 0) return NULL; if (ret == 0) free_more_memory(); } __find_get_block does not find the block, since it will not be marked as mapped, and so grow_buffers is called to fill in the buffers for the associated page. I believe the for (;;) loop is there primarily to retry in the case of memory pressure keeping grow_buffers from succeeding. However, we also continue to loop for other cases, like the block lying beond the end of the disk. So, the fix I came up with is to only loop when grow_buffers fails due to memory allocation issues (return value of 0). The attached patch was tested by myself, Torsten, and Rich, and was found to resolve the problem in call cases. Signed-off-by: Jeff Moyer <jmoyer@redhat.com> Reported-and-Tested-by: Torsten Hilbrich <torsten.hilbrich@secunet.com> Tested-by: Richard W.M. Jones <rjones@redhat.com> Reviewed-by: Josh Boyer <jwboyer@redhat.com> Cc: Stable <stable@vger.kernel.org> # 3.0+ [ Jens is on vacation, taking this directly - Linus ] -- Stable Notes: this patch requires backport to 3.0, 3.2 and 3.3. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/buffer.c22
1 files changed, 13 insertions, 9 deletions
diff --git a/fs/buffer.c b/fs/buffer.c
index 838a9cf246bd..c7062c896d7c 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1036,6 +1036,9 @@ grow_buffers(struct block_device *bdev, sector_t block, int size)
static struct buffer_head *
__getblk_slow(struct block_device *bdev, sector_t block, int size)
{
+ int ret;
+ struct buffer_head *bh;
+
/* Size must be multiple of hard sectorsize */
if (unlikely(size & (bdev_logical_block_size(bdev)-1) ||
(size < 512 || size > PAGE_SIZE))) {
@@ -1048,20 +1051,21 @@ __getblk_slow(struct block_device *bdev, sector_t block, int size)
return NULL;
}
- for (;;) {
- struct buffer_head * bh;
- int ret;
+retry:
+ bh = __find_get_block(bdev, block, size);
+ if (bh)
+ return bh;
+ ret = grow_buffers(bdev, block, size);
+ if (ret == 0) {
+ free_more_memory();
+ goto retry;
+ } else if (ret > 0) {
bh = __find_get_block(bdev, block, size);
if (bh)
return bh;
-
- ret = grow_buffers(bdev, block, size);
- if (ret < 0)
- return NULL;
- if (ret == 0)
- free_more_memory();
}
+ return NULL;
}
/*