From 151ff9325e5e17c97839a00b740726656b04647b Mon Sep 17 00:00:00 2001 From: Zhang Yi Date: Wed, 23 Apr 2025 16:52:52 +0800 Subject: [PATCH] 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 Link: https://patch.msgid.link/20250423085257.122685-5-yi.zhang@huaweicloud.com Signed-off-by: Theodore Ts'o --- fs/ext4/extents.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index 8a5724b2dc51..3adf05fbdd59 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -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, -- 2.50.1