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Message-Id: <20250601233744.3514795-26-sashal@kernel.org>
Date: Sun, 1 Jun 2025 19:37:03 -0400
From: Sasha Levin <sashal@...nel.org>
To: patches@...ts.linux.dev,
stable@...r.kernel.org
Cc: Zhang Yi <yi.zhang@...wei.com>,
Theodore Ts'o <tytso@....edu>,
Sasha Levin <sashal@...nel.org>,
adilger.kernel@...ger.ca,
linux-ext4@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH AUTOSEL 6.6 26/66] ext4: ext4: unify EXT4_EX_NOCACHE|NOFAIL flags in ext4_ext_remove_space()
From: Zhang Yi <yi.zhang@...wei.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@...wei.com>
Link: https://patch.msgid.link/20250423085257.122685-2-yi.zhang@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Sasha Levin <sashal@...nel.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 32218ac7f50fe..b3635254844c8 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -1536,7 +1536,7 @@ 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;
@@ -1610,7 +1610,8 @@ 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);
@@ -1618,7 +1619,7 @@ 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);
@@ -2799,6 +2800,7 @@ 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;
@@ -2829,8 +2831,7 @@ 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);
@@ -2895,7 +2896,7 @@ 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) {
@@ -2972,8 +2973,7 @@ 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);
@@ -4272,7 +4272,8 @@ 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;
--
2.39.5
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