[PATCH 5.15 229/570] ext4: fix dirtyclusters double decrement on fs shutdown

Greg Kroah-Hartman
2026-04-13T16:29:06Z

From: Brian Foster <bfoster@redhat.com>

[ Upstream commit 94a8cea54cd935c54fa2fba70354757c0fc245e3 ]

fstests test generic/388 occasionally reproduces a warning in
ext4_put_super() associated with the dirty clusters count:

WARNING: CPU: 7 PID: 76064 at fs/ext4/super.c:1324 ext4_put_super+0x48c/0x590 [ext4]

Tracing the failure shows that the warning fires due to an
s_dirtyclusters_counter value of -1. IOW, this appears to be a
spurious decrement as opposed to some sort of leak. Further tracing
of the dirty cluster count deltas and an LLM scan of the resulting
output identified the cause as a double decrement in the error path
between ext4_mb_mark_diskspace_used() and the caller
ext4_mb_new_blocks().

First, note that generic/388 is a shutdown vs. fsstress test and so
produces a random set of operations and shutdown injections. In the
problematic case, the shutdown triggers an error return from the
ext4_handle_dirty_metadata() call(s) made from
ext4_mb_mark_context(). The changed value is non-zero at this point,
so ext4_mb_mark_diskspace_used() does not exit after the error
bubbles up from ext4_mb_mark_context(). Instead, the former
decrements both cluster counters and returns the error up to
ext4_mb_new_blocks(). The latter falls into the !ar->len out path
which decrements the dirty clusters counter a second time, creating
the inconsistency.

To avoid this problem and simplify ownership of the cluster
reservation in this codepath, lift the counter reduction to a single
place in the caller. This makes it more clear that
ext4_mb_new_blocks() is responsible for acquiring cluster
reservation (via ext4_claim_free_clusters()) in the !delalloc case
as well as releasing it, regardless of whether it ends up consumed
or returned due to failure.

Fixes: 0087d9fb3f29 ("ext4: Fix s_dirty_blocks_counter if block allocation failed with nodelalloc")
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Baokun Li <libaokun1@huawei.com>
Link: https://patch.msgid.link/20260113171905.118284-1-bfoster@redhat.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
[ Drop mballoc-test changes ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/ext4/mballoc.c | 21 +++++----------------
1 file changed, 5 insertions(+), 16 deletions(-)

--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3834,8 +3834,7 @@ void ext4_exit_mballoc(void)
* Returns 0 if success or error code
*/
static noinline_for_stack int
-ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
- handle_t *handle, unsigned int reserv_clstrs)
+ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac, handle_t *handle)
{
struct buffer_head *bitmap_bh = NULL;
struct ext4_group_desc *gdp;
@@ -3923,13 +3922,6 @@ ext4_mb_mark_diskspace_used(struct ext4_

ext4_unlock_group(sb, ac->ac_b_ex.fe_group);
percpu_counter_sub(&sbi->s_freeclusters_counter, ac->ac_b_ex.fe_len);
- /*
- * Now reduce the dirty block count also. Should not go negative
- */
- if (!(ac->ac_flags & EXT4_MB_DELALLOC_RESERVED))
- /* release all the reserved blocks if non delalloc */
- percpu_counter_sub(&sbi->s_dirtyclusters_counter,
- reserv_clstrs);

if (sbi->s_log_groups_per_flex) {
ext4_group_t flex_group = ext4_flex_group(sbi,
@@ -5801,7 +5793,7 @@ repeat:
ext4_mb_pa_free(ac);
}
if (likely(ac->ac_status == AC_STATUS_FOUND)) {
- *errp = ext4_mb_mark_diskspace_used(ac, handle, reserv_clstrs);
+ *errp = ext4_mb_mark_diskspace_used(ac, handle);
if (*errp) {
ext4_discard_allocated_blocks(ac);
goto errout;
@@ -5833,12 +5825,9 @@ out:
kmem_cache_free(ext4_ac_cachep, ac);
if (inquota && ar->len < inquota)
dquot_free_block(ar->inode, EXT4_C2B(sbi, inquota - ar->len));
- if (!ar->len) {
- if ((ar->flags & EXT4_MB_DELALLOC_RESERVED) == 0)
- /* release all the reserved blocks if non delalloc */
- percpu_counter_sub(&sbi->s_dirtyclusters_counter,
- reserv_clstrs);
- }
+ /* release any reserved blocks */
+ if (reserv_clstrs)
+ percpu_counter_sub(&sbi->s_dirtyclusters_counter, reserv_clstrs);

trace_ext4_allocate_blocks(ar, (unsigned long long)block);