Commit 151ff932 authored by Zhang Yi's avatar Zhang Yi Committed by Theodore Ts'o
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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: default avatarZhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20250423085257.122685-5-yi.zhang@huaweicloud.com


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 402e38e6

fs/ext4/extents.c

+11 −6
Original line number Diff line number Diff line
@@ -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,

		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,