[PATCH 6.18 268/309] ext4: fix the might_sleep() warnings in kvfree()

Greg Kroah-Hartman
2026-03-31T17:08:15Z

From: Zqiang <qiang.zhang@linux.dev>

commit 496bb99b7e66f48b178126626f47e9ba79e2d0fa upstream.

Use the kvfree() in the RCU read critical section can trigger
the following warnings:

EXT4-fs (vdb): unmounting filesystem cd983e5b-3c83-4f5a-a136-17b00eb9d018.

WARNING: suspicious RCU usage

./include/linux/rcupdate.h:409 Illegal context switch in RCU read-side critical section!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1

Call Trace:
<TASK>
dump_stack_lvl+0xbb/0xd0
dump_stack+0x14/0x20
lockdep_rcu_suspicious+0x15a/0x1b0
__might_resched+0x375/0x4d0
? put_object.part.0+0x2c/0x50
__might_sleep+0x108/0x160
vfree+0x58/0x910
? ext4_group_desc_free+0x27/0x270
kvfree+0x23/0x40
ext4_group_desc_free+0x111/0x270
ext4_put_super+0x3c8/0xd40
generic_shutdown_super+0x14c/0x4a0
? __pfx_shrinker_free+0x10/0x10
kill_block_super+0x40/0x90
ext4_kill_sb+0x6d/0xb0
deactivate_locked_super+0xb4/0x180
deactivate_super+0x7e/0xa0
cleanup_mnt+0x296/0x3e0
__cleanup_mnt+0x16/0x20
task_work_run+0x157/0x250
? __pfx_task_work_run+0x10/0x10
? exit_to_user_mode_loop+0x6a/0x550
exit_to_user_mode_loop+0x102/0x550
do_syscall_64+0x44a/0x500
entry_SYSCALL_64_after_hwframe+0x77/0x7f
</TASK>

BUG: sleeping function called from invalid context at mm/vmalloc.c:3441
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 556, name: umount
preempt_count: 1, expected: 0
CPU: 3 UID: 0 PID: 556 Comm: umount
Call Trace:
<TASK>
dump_stack_lvl+0xbb/0xd0
dump_stack+0x14/0x20
__might_resched+0x275/0x4d0
? put_object.part.0+0x2c/0x50
__might_sleep+0x108/0x160
vfree+0x58/0x910
? ext4_group_desc_free+0x27/0x270
kvfree+0x23/0x40
ext4_group_desc_free+0x111/0x270
ext4_put_super+0x3c8/0xd40
generic_shutdown_super+0x14c/0x4a0
? __pfx_shrinker_free+0x10/0x10
kill_block_super+0x40/0x90
ext4_kill_sb+0x6d/0xb0
deactivate_locked_super+0xb4/0x180
deactivate_super+0x7e/0xa0
cleanup_mnt+0x296/0x3e0
__cleanup_mnt+0x16/0x20
task_work_run+0x157/0x250
? __pfx_task_work_run+0x10/0x10
? exit_to_user_mode_loop+0x6a/0x550
exit_to_user_mode_loop+0x102/0x550
do_syscall_64+0x44a/0x500
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The above scenarios occur in initialization failures and teardown
paths, there are no parallel operations on the resources released
by kvfree(), this commit therefore remove rcu_read_lock/unlock() and
use rcu_access_pointer() instead of rcu_dereference() operations.

Fixes: 7c990728b99e ("ext4: fix potential race between s_flex_groups online resizing and access")
Fixes: df3da4ea5a0f ("ext4: fix potential race between s_group_info online resizing and access")
Signed-off-by: Zqiang <qiang.zhang@linux.dev>
Reviewed-by: Baokun Li <libaokun@linux.alibaba.com>
Link: https://patch.msgid.link/20260319094545.19291-1-qiang.zhang@linux.dev
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/ext4/mballoc.c | 10 +++-------
fs/ext4/super.c | 8 ++------
2 files changed, 5 insertions(+), 13 deletions(-)

--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3579,9 +3579,7 @@ err_freebuddy:
rcu_read_unlock();
iput(sbi->s_buddy_cache);
err_freesgi:
- rcu_read_lock();
- kvfree(rcu_dereference(sbi->s_group_info));
- rcu_read_unlock();
+ kvfree(rcu_access_pointer(sbi->s_group_info));
return -ENOMEM;
}

@@ -3898,7 +3896,8 @@ void ext4_mb_release(struct super_block
WARN_ON_ONCE(!list_empty(&sbi->s_discard_list));
}

- if (sbi->s_group_info) {
+ group_info = rcu_access_pointer(sbi->s_group_info);
+ if (group_info) {
for (i = 0; i < ngroups; i++) {
cond_resched();
grinfo = ext4_get_group_info(sb, i);
@@ -3916,12 +3915,9 @@ void ext4_mb_release(struct super_block
num_meta_group_infos = (ngroups +
EXT4_DESC_PER_BLOCK(sb) - 1) >>
EXT4_DESC_PER_BLOCK_BITS(sb);
- rcu_read_lock();
- group_info = rcu_dereference(sbi->s_group_info);
for (i = 0; i < num_meta_group_infos; i++)
kfree(group_info[i]);
kvfree(group_info);
- rcu_read_unlock();
}
ext4_mb_avg_fragment_size_destroy(sbi);
ext4_mb_largest_free_orders_destroy(sbi);
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1249,12 +1249,10 @@ static void ext4_group_desc_free(struct
struct buffer_head **group_desc;
int i;

- rcu_read_lock();
- group_desc = rcu_dereference(sbi->s_group_desc);
+ group_desc = rcu_access_pointer(sbi->s_group_desc);
for (i = 0; i < sbi->s_gdb_count; i++)
brelse(group_desc[i]);
kvfree(group_desc);
- rcu_read_unlock();
}

static void ext4_flex_groups_free(struct ext4_sb_info *sbi)
@@ -1262,14 +1260,12 @@ static void ext4_flex_groups_free(struct
struct flex_groups **flex_groups;
int i;

- rcu_read_lock();
- flex_groups = rcu_dereference(sbi->s_flex_groups);
+ flex_groups = rcu_access_pointer(sbi->s_flex_groups);
if (flex_groups) {
for (i = 0; i < sbi->s_flex_groups_allocated; i++)
kvfree(flex_groups[i]);
kvfree(flex_groups);
}
- rcu_read_unlock();
}

static void ext4_put_super(struct super_block *sb)