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buffer: fix unintended successful return 

If try_to_free_buffers() succeeded and then folio_alloc_buffers() failed,
grow_dev_folio() would return success.  This would be incorrect; memory
allocation failure is supposed to result in a failure.  It's a harmless
bug; the caller will simply go around the loop one more time and
grow_dev_folio() will correctly return a failure that time.  But it was an
unintended change and looks like a more serious bug than it is.

While I'm in here, improve the commentary about why we return success even
though we failed.

Link: https://lkml.kernel.org/r/20240101093848.2017115-1-willy@infradead.org
Fixes: 6d840a1877 ("buffer: return bool from grow_dev_folio()")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reported-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Matthew Wilcox (Oracle) 2024-01-01 09:38:48 +00:00 committed by Andrew Morton
parent 501a06fe8e
commit bcd30d4cd9
1 changed files with 12 additions and 5 deletions
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17
fs/buffer.c
View File

@ -1028,8 +1028,8 @@ static sector_t folio_init_buffers(struct folio *folio,
*
* This is used purely for blockdev mappings.
*
* Returns false if we have a 'permanent' failure. Returns true if
* we succeeded, or the caller should retry.
* Returns false if we have a failure which cannot be cured by retrying
* without sleeping. Returns true if we succeeded, or the caller should retry.
*/
static bool grow_dev_folio(struct block_device *bdev, sector_t block,
pgoff_t index, unsigned size, gfp_t gfp)
@ -1051,10 +1051,17 @@ static bool grow_dev_folio(struct block_device *bdev, sector_t block,
goto unlock;
}
/* Caller should retry if this call fails */
end_block = ~0ULL;
if (!try_to_free_buffers(folio))
/*
* Retrying may succeed; for example the folio may finish
* writeback, or buffers may be cleaned. This should not
* happen very often; maybe we have old buffers attached to
* this blockdev's page cache and we're trying to change
* the block size?
*/
if (!try_to_free_buffers(folio)) {
end_block = ~0ULL;
goto unlock;
}
}
bh = folio_alloc_buffers(folio, size, gfp | __GFP_ACCOUNT);