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ext4: prevent stale extent cache entries caused by concurrent fiemap 

The ext4_fiemap() currently invokes ext4_ext_precache() and
iomap_fiemap() to preload the extent cache and query mapping information
without holding the inode's i_rwsem. This can result in stale extent
cache entries when competing with operations such as
ext4_collapse_range() which calls ext4_ext_remove_space() or
ext4_ext_shift_extents().

The problem arises when ext4_ext_remove_space() temporarily releases
i_data_sem due to insufficient journal credits. During this interval, a
concurrent ext4_fiemap() may cache extent entries that are about to be
deleted. As a result, these cached entries become stale and inconsistent
with the actual extents.

Loading the extents cache without holding the inode's i_rwsem or the
mapping's invalidate_lock is not permitted besides during the writeback.
Fix this by holding the i_rwsem in ext4_fiemap().

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20250423085257.122685-5-yi.zhang@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Zhang Yi 2025-04-23 16:52:52 +08:00 committed by Theodore Ts'o
parent 402e38e6b7
commit 151ff9325e
1 changed files with 11 additions and 6 deletions
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17
fs/ext4/extents.c
View File

@ -4963,10 +4963,11 @@ int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
{
int error = 0;
inode_lock_shared(inode);
if (fieinfo->fi_flags & FIEMAP_FLAG_CACHE) {
error = ext4_ext_precache(inode);
if (error)
return error;
goto unlock;
fieinfo->fi_flags &= ~FIEMAP_FLAG_CACHE;
}
@ -4977,15 +4978,19 @@ int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
*/
error = ext4_fiemap_check_ranges(inode, start, &len);
if (error)
return error;
goto unlock;
if (fieinfo->fi_flags & FIEMAP_FLAG_XATTR) {
fieinfo->fi_flags &= ~FIEMAP_FLAG_XATTR;
return iomap_fiemap(inode, fieinfo, start, len,
&ext4_iomap_xattr_ops);
error = iomap_fiemap(inode, fieinfo, start, len,
&ext4_iomap_xattr_ops);
} else {
error = iomap_fiemap(inode, fieinfo, start, len,
&ext4_iomap_report_ops);
}
return iomap_fiemap(inode, fieinfo, start, len, &ext4_iomap_report_ops);
unlock:
inode_unlock_shared(inode);
return error;
}
int ext4_get_es_cache(struct inode *inode, struct fiemap_extent_info *fieinfo,