From: Zhang Yi yi.zhang@huawei.com
[ Upstream commit 53ce42accd2002cc490fc86000ac532530507a74 ]
When removing space, we should use EXT4_EX_NOCACHE because we don't need to cache extents, and we should also use EXT4_EX_NOFAIL to prevent metadata inconsistencies that may arise from memory allocation failures. While ext4_ext_remove_space() already uses these two flags in most places, they are missing in ext4_ext_search_right() and read_extent_tree_block() calls. Unify the flags to ensure consistent behavior throughout the extent removal process.
Signed-off-by: Zhang Yi yi.zhang@huawei.com Link: https://patch.msgid.link/20250423085257.122685-2-yi.zhang@huaweicloud.com Signed-off-by: Theodore Ts'o tytso@mit.edu Signed-off-by: Sasha Levin sashal@kernel.org ---
Based on my thorough analysis of this commit and the kernel code context, here is my assessment: **YES** This commit should be backported to stable kernel trees. ## Detailed Analysis: ### **Nature of the Bug Fix** This commit addresses an important consistency issue in the ext4 extent removal process. The problem is that `ext4_ext_remove_space()` inconsistently applies critical flags (`EXT4_EX_NOCACHE | EXT4_EX_NOFAIL`) across all its `read_extent_tree_block()` calls. ### **Technical Impact** 1. **`EXT4_EX_NOCACHE`**: Prevents caching of extents during removal operations. Without this flag in `ext4_ext_search_right()` calls (lines 1607, 1615), the extent cache could become polluted with stale entries during space removal, potentially leading to incorrect block mappings. 2. **`EXT4_EX_NOFAIL`**: Ensures memory allocation cannot fail during critical metadata operations. The absence of this flag in the affected calls could cause metadata inconsistencies if memory allocation fails during extent tree traversal. ### **Risk Assessment - Low Risk** - **Small, contained change**: Only adds consistent flag usage across existing function calls - **No algorithmic changes**: The core logic remains unchanged - **Well-understood flags**: Both flags are already used extensively in the same function ### **Comparison with Historical Commits** **Similar to "YES" commits:** - Like commit #1 (ext4 cache pollution fix): Addresses extent cache consistency issues - Like commit #2 (nofail preallocation): Prevents metadata inconsistencies from allocation failures - Small, targeted fix with clear purpose - Addresses potential data corruption scenarios **Unlike "NO" commits:** - Not a cleanup/refactoring (commits #3, #4, #5 were architectural changes) - Not removing functionality or making API changes - Fixes an actual bug rather than just code organization ### **Code Evidence** The changes are in `/fs/ext4/extents.c:1607, 1615, 2980, 2920, 4299`: 1. **Lines 1607, 1615**: `ext4_ext_search_right()` now receives and uses flags parameter 2. **Line 2980**: `read_extent_tree_block()` in the main removal loop now uses unified flags 3. **Line 2920**: `ext4_ext_search_right()` call now passes flags consistently 4. **Line 4299**: Non-removal path correctly passes 0 flags (no change in behavior) ### **Subsystem Context** From examining the kernel source: - `EXT4_EX_NOCACHE` prevents extent caching when `depth == 0` (line ~460 in extents.c) - `EXT4_EX_NOFAIL` adds `__GFP_NOFAIL` to allocation flags (line ~397 in extents.c) - The function `ext4_ext_remove_space()` is called during truncation and punch hole operations ### **User Impact** This fixes potential filesystem corruption during: - File truncation operations - Punch hole operations - Any extent removal scenarios The inconsistent flag usage could lead to stale extent cache entries and allocation failures during critical metadata operations, both of which can cause filesystem corruption. ### **Conclusion** This is a clear bug fix that prevents potential filesystem corruption with minimal risk of regression. It follows the pattern of similar commits that were successfully backported and addresses a real consistency issue that could affect filesystem reliability.
fs/ext4/extents.c | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-)
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index ba3419958a832..4d7729321c80e 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -1530,7 +1530,7 @@ static int ext4_ext_search_left(struct inode *inode, static int ext4_ext_search_right(struct inode *inode, struct ext4_ext_path *path, ext4_lblk_t *logical, ext4_fsblk_t *phys, - struct ext4_extent *ret_ex) + struct ext4_extent *ret_ex, int flags) { struct buffer_head *bh = NULL; struct ext4_extent_header *eh; @@ -1604,7 +1604,8 @@ static int ext4_ext_search_right(struct inode *inode, ix++; while (++depth < path->p_depth) { /* subtract from p_depth to get proper eh_depth */ - bh = read_extent_tree_block(inode, ix, path->p_depth - depth, 0); + bh = read_extent_tree_block(inode, ix, path->p_depth - depth, + flags); if (IS_ERR(bh)) return PTR_ERR(bh); eh = ext_block_hdr(bh); @@ -1612,7 +1613,7 @@ static int ext4_ext_search_right(struct inode *inode, put_bh(bh); }
- bh = read_extent_tree_block(inode, ix, path->p_depth - depth, 0); + bh = read_extent_tree_block(inode, ix, path->p_depth - depth, flags); if (IS_ERR(bh)) return PTR_ERR(bh); eh = ext_block_hdr(bh); @@ -2821,6 +2822,7 @@ int ext4_ext_remove_space(struct inode *inode, ext4_lblk_t start, struct partial_cluster partial; handle_t *handle; int i = 0, err = 0; + int flags = EXT4_EX_NOCACHE | EXT4_EX_NOFAIL;
partial.pclu = 0; partial.lblk = 0; @@ -2851,8 +2853,7 @@ int ext4_ext_remove_space(struct inode *inode, ext4_lblk_t start, ext4_fsblk_t pblk;
/* find extent for or closest extent to this block */ - path = ext4_find_extent(inode, end, NULL, - EXT4_EX_NOCACHE | EXT4_EX_NOFAIL); + path = ext4_find_extent(inode, end, NULL, flags); if (IS_ERR(path)) { ext4_journal_stop(handle); return PTR_ERR(path); @@ -2918,7 +2919,7 @@ int ext4_ext_remove_space(struct inode *inode, ext4_lblk_t start, */ lblk = ex_end + 1; err = ext4_ext_search_right(inode, path, &lblk, &pblk, - NULL); + NULL, flags); if (err < 0) goto out; if (pblk) { @@ -2994,8 +2995,7 @@ int ext4_ext_remove_space(struct inode *inode, ext4_lblk_t start, i + 1, ext4_idx_pblock(path[i].p_idx)); memset(path + i + 1, 0, sizeof(*path)); bh = read_extent_tree_block(inode, path[i].p_idx, - depth - i - 1, - EXT4_EX_NOCACHE); + depth - i - 1, flags); if (IS_ERR(bh)) { /* should we reset i_size? */ err = PTR_ERR(bh); @@ -4314,7 +4314,8 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode, if (err) goto out; ar.lright = map->m_lblk; - err = ext4_ext_search_right(inode, path, &ar.lright, &ar.pright, &ex2); + err = ext4_ext_search_right(inode, path, &ar.lright, &ar.pright, + &ex2, 0); if (err < 0) goto out;