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ext4: drop extent cache after doing PARTIAL_VALID1 zeroout

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When splitting an unwritten extent in the middle and converting it to
initialized in ext4_split_extent() with the EXT4_EXT_MAY_ZEROOUT and
EXT4_EXT_DATA_VALID2 flags set, it could leave a stale unwritten extent.

Assume we have an unwritten file and buffered write in the middle of it
without dioread_nolock enabled, it will allocate blocks as written
extent.

       0  A      B  N
       [UUUUUUUUUUUU] on-disk extent      U: unwritten extent
       [UUUUUUUUUUUU] extent status tree
       [--DDDDDDDD--]                     D: valid data
          |<-  ->| ----> this range needs to be initialized

ext4_split_extent() first try to split this extent at B with
EXT4_EXT_DATA_PARTIAL_VALID1 and EXT4_EXT_MAY_ZEROOUT flag set, but
ext4_split_extent_at() failed to split this extent due to temporary lack
of space. It zeroout B to N and leave the entire extent as unwritten.

       0  A      B  N
       [UUUUUUUUUUUU] on-disk extent
       [UUUUUUUUUUUU] extent status tree
       [--DDDDDDDDZZ]                     Z: zeroed data

ext4_split_extent() then try to split this extent at A with
EXT4_EXT_DATA_VALID2 flag set. This time, it split successfully and
leave an written extent from A to N.

       0  A      B  N
       [UUWWWWWWWWWW] on-disk extent      W: written extent
       [UUUUUUUUUUUU] extent status tree
       [--DDDDDDDDZZ]

Finally ext4_map_create_blocks() only insert extent A to B to the extent
status tree, and leave an stale unwritten extent in the status tree.

       0  A      B  N
       [UUWWWWWWWWWW] on-disk extent      W: written extent
       [UUWWWWWWWWUU] extent status tree
       [--DDDDDDDDZZ]

Fix this issue by always cached extent status entry after zeroing out
the second part.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Baokun Li <libaokun1@huawei.com>
Cc: stable@kernel.org
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Message-ID: <20251129103247.686136-7-yi.zhang@huaweicloud.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Zhang Yi 2025-11-29 18:32:38 +08:00 committed by Theodore Ts'o
parent 8b4b19a2f9
commit 6d882ea3b0
1 changed files with 9 additions and 1 deletions
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10
fs/ext4/extents.c
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@ -3319,8 +3319,16 @@ static struct ext4_ext_path *ext4_split_extent_at(handle_t *handle,
* extent length and ext4_split_extent() split will the
* first half again.
*/
if (split_flag & EXT4_EXT_DATA_PARTIAL_VALID1)
if (split_flag & EXT4_EXT_DATA_PARTIAL_VALID1) {
/*
* Drop extent cache to prevent stale unwritten
* extents remaining after zeroing out.
*/
ext4_es_remove_extent(inode,
le32_to_cpu(zero_ex.ee_block),
ext4_ext_get_actual_len(&zero_ex));
goto fix_extent_len;
}
/* update the extent length and mark as initialized */
ex->ee_len = cpu_to_le16(ee_len);