Jeff,
Your commit 91f68c89d8f3 ("block: fix infinite loop in __getblk_slow"),
already gone into 3.* stable, is not good. Could you and your testers
please give this alternative a try - I think it should work, and have
started it on a few days' memory load on 3.5, but not tried your case.
But, see final paragraph of comment below, I'm worried whether
all __getblk() users are actually ready for your new NULL case.
Thanks,
Hugh
[PATCH] block: replace __getblk_slow misfix by grow_dev_page fix
Commit 91f68c89d8f3 ("block: fix infinite loop in __getblk_slow")
is not good: a successful call to grow_buffers() cannot guarantee
that the page won't be reclaimed before the immediate next call to
__find_get_block(), which is why there was always a loop there.
Yesterday I got "EXT4-fs error (device loop0): __ext4_get_inode_loc:3595:
inode #19278: block 664: comm cc1: unable to read itable block" on console,
which pointed to this commit.
I've been trying to bisect for weeks, why kbuild-on-ext4-on-loop-on-tmpfs
sometimes fails from a missing header file, under memory pressure on
ppc G5. I've never seen this on x86, and I've never seen it on 3.5-rc7
itself, despite that commit being in there: bisection pointed to an
irrelevant pinctrl merge, but hard to tell when failure takes between
18 minutes and 38 hours (but so far it's happened quicker on 3.6-rc2).
(I've since found such __ext4_get_inode_loc errors in /var/log/messages
from previous weeks: why the message never appeared on console until
yesterday morning is a mystery for another day.)
Revert 91f68c89d8f3, restoring __getblk_slow() to how it was (plus
a checkpatch nitfix). Avoid the infinite loop beyond end of device
by instead checking buffer_mapped(bh) in grow_dev_page() (I presume
that's more efficient than a repeated call to blkdev_max_block()),
and returning -ENXIO to __getblk_slow() in that case.
And remove akpm's ten-year-old "__getblk() cannot fail ... weird"
comment, but that is worrying: are all users of __getblk() really
now prepared for a NULL bh beyond end of device, or will some oops??
Signed-off-by: Hugh Dickins <hu...@google.com>
Cc: sta...@vger.kernel.org # 3.0 3.2 3.4 3.5
---
fs/buffer.c | 43 +++++++++++++++++++++----------------------
1 file changed, 21 insertions(+), 22 deletions(-)
--- 3.6-rc2/fs/buffer.c 2012-08-04 09:19:20.644022328 -0700
+++ linux/fs/buffer.c 2012-08-21 08:49:32.333908590 -0700
@@ -950,6 +950,7 @@ grow_dev_page(struct block_device *bdev,
struct inode *inode = bdev->bd_inode;
struct page *page;
struct buffer_head *bh;
+ int err = 0;
page = find_or_create_page(inode->i_mapping, index,
(mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS)|__GFP_MOVABLE);
@@ -962,7 +963,11 @@ grow_dev_page(struct block_device *bdev,
bh = page_buffers(page);
if (bh->b_size == size) {
init_page_buffers(page, bdev, block, size);
- return page;
+ if (buffer_mapped(bh))
+ return page;
+
+ err = -ENXIO;
+ goto failed;
}
if (!try_to_free_buffers(page))
goto failed;
@@ -984,12 +989,14 @@ grow_dev_page(struct block_device *bdev,
link_dev_buffers(page, bh);
init_page_buffers(page, bdev, block, size);
spin_unlock(&inode->i_mapping->private_lock);
- return page;
+ if (buffer_mapped(bh))
+ return page;
+ err = -ENXIO;
failed:
unlock_page(page);
page_cache_release(page);
- return NULL;
+ return ERR_PTR(err);
}
/*
@@ -1026,8 +1033,8 @@ grow_buffers(struct block_device *bdev,
block = index << sizebits;
/* Create a page with the proper size buffers.. */
page = grow_dev_page(bdev, block, index, size);
- if (!page)
- return 0;
+ if (IS_ERR_OR_NULL(page))
+ return PTR_RET(page);
unlock_page(page);
page_cache_release(page);
return 1;
@@ -1036,9 +1043,6 @@ grow_buffers(struct block_device *bdev,
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))) {
@@ -1051,21 +1055,20 @@ __getblk_slow(struct block_device *bdev,
return NULL;
}
-retry:
- bh = __find_get_block(bdev, block, size);
- if (bh)
- return bh;
+ for (;;) {
+ struct buffer_head *bh;
+ int ret;
- 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;
}
/*
@@ -1321,10 +1324,6 @@ EXPORT_SYMBOL(__find_get_block);
* which corresponds to the passed block_device, block and size. The
* returned buffer has its reference count incremented.
*
- * __getblk() cannot fail - it just keeps trying. If you pass it an
- * illegal block number, __getblk() will happily return a buffer_head
- * which represents the non-existent block. Very weird.
- *
* __getblk() will lock up the machine if grow_dev_page's try_to_free_buffers()
* attempt is failing. FIXME, perhaps?
*/
--
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