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.
Reported-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
fs/buffer.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/fs/buffer.c b/fs/buffer.c
index d5ce6b29c893..d3bcf601d3e5 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -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);
--
2.43.0
