Commit f22a0ef2 authored by Zhang Yi's avatar Zhang Yi Committed by Theodore Ts'o
Browse files

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: default avatarZhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20250423085257.122685-6-yi.zhang@huaweicloud.com


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 151ff932

fs/ext4/extents.c

+2 −0
Original line number Diff line number Diff line
@@ -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;

fs/ext4/ioctl.c

+7 −1
Original line number Diff line number Diff line
@@ -1505,8 +1505,14 @@ static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) 
		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;