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ext4: prevent stale extent cache entries caused by concurrent get es_cache 

The EXT4_IOC_GET_ES_CACHE and EXT4_IOC_PRECACHE_EXTENTS currently
invokes ext4_ext_precache() to preload the extent cache 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_IOC_GET_ES_CACHE or EXT4_IOC_PRECACHE_EXTENTS 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 during EXT4_IOC_GET_ES_CACHE and
EXT4_IOC_PRECACHE_EXTENTS.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20250423085257.122685-6-yi.zhang@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Zhang Yi 2025-04-23 16:52:53 +08:00 committed by Theodore Ts'o
parent 151ff9325e
commit f22a0ef223
2 changed files with 9 additions and 1 deletions
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2
fs/ext4/extents.c
View File

@ -5011,7 +5011,9 @@ int ext4_get_es_cache(struct inode *inode, struct fiemap_extent_info *fieinfo,
}
if (fieinfo->fi_flags & FIEMAP_FLAG_CACHE) {
inode_lock_shared(inode);
error = ext4_ext_precache(inode);
inode_unlock_shared(inode);
if (error)
return error;
fieinfo->fi_flags &= ~FIEMAP_FLAG_CACHE;

8
fs/ext4/ioctl.c
View File

@ -1505,8 +1505,14 @@ resizefs_out:
return 0;
}
case EXT4_IOC_PRECACHE_EXTENTS:
return ext4_ext_precache(inode);
{
int ret;
inode_lock_shared(inode);
ret = ext4_ext_precache(inode);
inode_unlock_shared(inode);
return ret;
}
case FS_IOC_SET_ENCRYPTION_POLICY:
if (!ext4_has_feature_encrypt(sb))
return -EOPNOTSUPP;