[syzbot] possible deadlock in start_this_handle (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 5a29232d870d Merge tag 'for-5.19-rc6-tag' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16619ce8080000
kernel config: https://syzkaller.appspot.com/x/.config?x=525bc0635a2b942a
dashboard link: https://syzkaller.appspot.com/bug?extid=2d2aeadc6ce1e1f11d45
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: i386

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2d2aea...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
5.19.0-rc6-syzkaller-00026-g5a29232d870d #0 Not tainted
------------------------------------------------------
khugepaged/48 is trying to acquire lock:
ffff888044598990 (jbd2_handle){++++}-{0:0}, at: start_this_handle+0xfb4/0x14a0 fs/jbd2/transaction.c:461

but task is already holding lock:
ffffffff8bebdb20 (fs_reclaim){+.+.}-{0:0}, at: __perform_reclaim mm/page_alloc.c:4638 [inline]
ffffffff8bebdb20 (fs_reclaim){+.+.}-{0:0}, at: __alloc_pages_direct_reclaim mm/page_alloc.c:4663 [inline]
ffffffff8bebdb20 (fs_reclaim){+.+.}-{0:0}, at: __alloc_pages_slowpath.constprop.0+0x9e1/0x2160 mm/page_alloc.c:5066

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (fs_reclaim){+.+.}-{0:0}:
__fs_reclaim_acquire mm/page_alloc.c:4589 [inline]
fs_reclaim_acquire+0x115/0x160 mm/page_alloc.c:4603
might_alloc include/linux/sched/mm.h:271 [inline]
slab_pre_alloc_hook mm/slab.h:723 [inline]
slab_alloc_node mm/slub.c:3157 [inline]
slab_alloc mm/slub.c:3251 [inline]
kmem_cache_alloc_trace+0x40/0x3f0 mm/slub.c:3282
kmalloc include/linux/slab.h:600 [inline]
memory_stat_format+0x95/0xae0 mm/memcontrol.c:1468
mem_cgroup_print_oom_meminfo.cold+0x50/0x7e mm/memcontrol.c:1594
dump_header+0x13f/0x7f9 mm/oom_kill.c:462
oom_kill_process.cold+0x10/0x15 mm/oom_kill.c:1037
out_of_memory+0x358/0x14b0 mm/oom_kill.c:1175
mem_cgroup_out_of_memory+0x206/0x270 mm/memcontrol.c:1650
memory_max_write+0x25c/0x3b0 mm/memcontrol.c:6299
cgroup_file_write+0x1de/0x770 kernel/cgroup/cgroup.c:3882
kernfs_fop_write_iter+0x3f8/0x610 fs/kernfs/file.c:290
call_write_iter include/linux/fs.h:2058 [inline]
new_sync_write+0x38a/0x560 fs/read_write.c:504
vfs_write+0x7c0/0xac0 fs/read_write.c:591
ksys_write+0x127/0x250 fs/read_write.c:644
do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]
__do_fast_syscall_32+0x65/0xf0 arch/x86/entry/common.c:178
do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:203
entry_SYSENTER_compat_after_hwframe+0x53/0x62

-> #1 (oom_lock){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x12f/0x1350 kernel/locking/mutex.c:747
mem_cgroup_out_of_memory+0x8d/0x270 mm/memcontrol.c:1640
mem_cgroup_oom mm/memcontrol.c:1880 [inline]
try_charge_memcg+0xef9/0x1380 mm/memcontrol.c:2670
obj_cgroup_charge_pages mm/memcontrol.c:2999 [inline]
obj_cgroup_charge+0x2ab/0x5e0 mm/memcontrol.c:3289
memcg_slab_pre_alloc_hook mm/slab.h:505 [inline]
slab_pre_alloc_hook mm/slab.h:728 [inline]
slab_alloc_node mm/slub.c:3157 [inline]
slab_alloc mm/slub.c:3251 [inline]
__kmem_cache_alloc_lru mm/slub.c:3258 [inline]
kmem_cache_alloc+0x92/0x3b0 mm/slub.c:3268
kmem_cache_zalloc include/linux/slab.h:723 [inline]
alloc_buffer_head+0x20/0x140 fs/buffer.c:3294
alloc_page_buffers+0x285/0x7a0 fs/buffer.c:829
grow_dev_page fs/buffer.c:965 [inline]
grow_buffers fs/buffer.c:1011 [inline]
__getblk_slow+0x525/0x1080 fs/buffer.c:1038
__getblk_gfp+0x6e/0x80 fs/buffer.c:1333
sb_getblk include/linux/buffer_head.h:326 [inline]
ext4_getblk+0x20d/0x7c0 fs/ext4/inode.c:866
ext4_bread+0x2a/0x1c0 fs/ext4/inode.c:912
ext4_append+0x177/0x3a0 fs/ext4/namei.c:67
ext4_init_new_dir+0x25e/0x4d0 fs/ext4/namei.c:2920
ext4_mkdir+0x3cf/0xb20 fs/ext4/namei.c:2966
vfs_mkdir+0x1c3/0x3b0 fs/namei.c:3975
do_mkdirat+0x285/0x300 fs/namei.c:4001
__do_sys_mkdirat fs/namei.c:4016 [inline]
__se_sys_mkdirat fs/namei.c:4014 [inline]
__ia32_sys_mkdirat+0x81/0xa0 fs/namei.c:4014
do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]
__do_fast_syscall_32+0x65/0xf0 arch/x86/entry/common.c:178
do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:203
entry_SYSENTER_compat_after_hwframe+0x53/0x62

-> #0 (jbd2_handle){++++}-{0:0}:
check_prev_add kernel/locking/lockdep.c:3095 [inline]
check_prevs_add kernel/locking/lockdep.c:3214 [inline]
validate_chain kernel/locking/lockdep.c:3829 [inline]
__lock_acquire+0x2abe/0x5660 kernel/locking/lockdep.c:5053
lock_acquire kernel/locking/lockdep.c:5665 [inline]
lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5630
start_this_handle+0xfe7/0x14a0 fs/jbd2/transaction.c:463
jbd2__journal_start+0x399/0x930 fs/jbd2/transaction.c:520
__ext4_journal_start_sb+0x3a8/0x4a0 fs/ext4/ext4_jbd2.c:105
__ext4_journal_start fs/ext4/ext4_jbd2.h:326 [inline]
ext4_dirty_inode+0x9d/0x110 fs/ext4/inode.c:5949
__mark_inode_dirty+0x495/0x1050 fs/fs-writeback.c:2381
mark_inode_dirty_sync include/linux/fs.h:2337 [inline]
iput.part.0+0x57/0x820 fs/inode.c:1767
iput+0x58/0x70 fs/inode.c:1760
dentry_unlink_inode+0x2b1/0x460 fs/dcache.c:401
__dentry_kill+0x3c0/0x640 fs/dcache.c:607
shrink_dentry_list+0x23c/0x800 fs/dcache.c:1201
prune_dcache_sb+0xe7/0x140 fs/dcache.c:1282
super_cache_scan+0x336/0x590 fs/super.c:104
do_shrink_slab+0x42d/0xbd0 mm/vmscan.c:770
shrink_slab+0x17c/0x6f0 mm/vmscan.c:930
shrink_node_memcgs mm/vmscan.c:3124 [inline]
shrink_node+0x8b3/0x1db0 mm/vmscan.c:3245
shrink_zones mm/vmscan.c:3482 [inline]
do_try_to_free_pages+0x3b5/0x1700 mm/vmscan.c:3540
try_to_free_pages+0x2ac/0x840 mm/vmscan.c:3775
__perform_reclaim mm/page_alloc.c:4641 [inline]
__alloc_pages_direct_reclaim mm/page_alloc.c:4663 [inline]
__alloc_pages_slowpath.constprop.0+0xa8a/0x2160 mm/page_alloc.c:5066
__alloc_pages+0x436/0x510 mm/page_alloc.c:5439
__alloc_pages_node include/linux/gfp.h:587 [inline]
khugepaged_alloc_page+0xa0/0x170 mm/khugepaged.c:859
collapse_huge_page mm/khugepaged.c:1062 [inline]
khugepaged_scan_pmd mm/khugepaged.c:1348 [inline]
khugepaged_scan_mm_slot mm/khugepaged.c:2170 [inline]
khugepaged_do_scan mm/khugepaged.c:2251 [inline]
khugepaged+0x3473/0x66a0 mm/khugepaged.c:2296
kthread+0x2e9/0x3a0 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:302

other info that might help us debug this:

Chain exists of:
jbd2_handle --> oom_lock --> fs_reclaim

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(fs_reclaim);
lock(oom_lock);
lock(fs_reclaim);
lock(jbd2_handle);

*** DEADLOCK ***

3 locks held by khugepaged/48:
#0: ffffffff8bebdb20 (fs_reclaim){+.+.}-{0:0}, at: __perform_reclaim mm/page_alloc.c:4638 [inline]
#0: ffffffff8bebdb20 (fs_reclaim){+.+.}-{0:0}, at: __alloc_pages_direct_reclaim mm/page_alloc.c:4663 [inline]
#0: ffffffff8bebdb20 (fs_reclaim){+.+.}-{0:0}, at: __alloc_pages_slowpath.constprop.0+0x9e1/0x2160 mm/page_alloc.c:5066
#1: ffffffff8be7d850 (shrinker_rwsem){++++}-{3:3}, at: shrink_slab+0xc9/0x6f0 mm/vmscan.c:920
#2: ffff8880445800e0 (&type->s_umount_key#33){++++}-{3:3}, at: trylock_super fs/super.c:415 [inline]
#2: ffff8880445800e0 (&type->s_umount_key#33){++++}-{3:3}, at: super_cache_scan+0x6c/0x590 fs/super.c:79

stack backtrace:
CPU: 2 PID: 48 Comm: khugepaged Not tainted 5.19.0-rc6-syzkaller-00026-g5a29232d870d #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2175
check_prev_add kernel/locking/lockdep.c:3095 [inline]
check_prevs_add kernel/locking/lockdep.c:3214 [inline]
validate_chain kernel/locking/lockdep.c:3829 [inline]
__lock_acquire+0x2abe/0x5660 kernel/locking/lockdep.c:5053
lock_acquire kernel/locking/lockdep.c:5665 [inline]
lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5630
start_this_handle+0xfe7/0x14a0 fs/jbd2/transaction.c:463
jbd2__journal_start+0x399/0x930 fs/jbd2/transaction.c:520
__ext4_journal_start_sb+0x3a8/0x4a0 fs/ext4/ext4_jbd2.c:105
__ext4_journal_start fs/ext4/ext4_jbd2.h:326 [inline]
ext4_dirty_inode+0x9d/0x110 fs/ext4/inode.c:5949
__mark_inode_dirty+0x495/0x1050 fs/fs-writeback.c:2381
mark_inode_dirty_sync include/linux/fs.h:2337 [inline]
iput.part.0+0x57/0x820 fs/inode.c:1767
iput+0x58/0x70 fs/inode.c:1760
dentry_unlink_inode+0x2b1/0x460 fs/dcache.c:401
__dentry_kill+0x3c0/0x640 fs/dcache.c:607
shrink_dentry_list+0x23c/0x800 fs/dcache.c:1201
prune_dcache_sb+0xe7/0x140 fs/dcache.c:1282
super_cache_scan+0x336/0x590 fs/super.c:104
do_shrink_slab+0x42d/0xbd0 mm/vmscan.c:770
shrink_slab+0x17c/0x6f0 mm/vmscan.c:930
shrink_node_memcgs mm/vmscan.c:3124 [inline]
shrink_node+0x8b3/0x1db0 mm/vmscan.c:3245
shrink_zones mm/vmscan.c:3482 [inline]
do_try_to_free_pages+0x3b5/0x1700 mm/vmscan.c:3540
try_to_free_pages+0x2ac/0x840 mm/vmscan.c:3775
__perform_reclaim mm/page_alloc.c:4641 [inline]
__alloc_pages_direct_reclaim mm/page_alloc.c:4663 [inline]
__alloc_pages_slowpath.constprop.0+0xa8a/0x2160 mm/page_alloc.c:5066
__alloc_pages+0x436/0x510 mm/page_alloc.c:5439
__alloc_pages_node include/linux/gfp.h:587 [inline]
khugepaged_alloc_page+0xa0/0x170 mm/khugepaged.c:859
collapse_huge_page mm/khugepaged.c:1062 [inline]
khugepaged_scan_pmd mm/khugepaged.c:1348 [inline]
khugepaged_scan_mm_slot mm/khugepaged.c:2170 [inline]
khugepaged_do_scan mm/khugepaged.c:2251 [inline]
khugepaged+0x3473/0x66a0 mm/khugepaged.c:2296
kthread+0x2e9/0x3a0 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:302
</TASK>


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[Jan Kara]

Hello,

so this lockdep report looks real but is more related to OOM handling than
to ext4 as such. The immediate problem I can see is that
mem_cgroup_print_oom_meminfo() which is called under oom_lock calls
memory_stat_format() which does GFP_KERNEL allocations to allocate buffers
for dumping of MM statistics. This creates oom_lock -> fs reclaim
dependency and because OOM can be hit (and thus oom_lock acquired) in
practically any allocation (regardless of GFP_NOFS) this has a potential of
creating real deadlock cycles.

So should mem_cgroup_print_oom_meminfo() be using
memalloc_nofs_save/restore() to avoid such deadlocks? Or perhaps someone
sees another solution? Generally allocating memory to report OOM looks a
bit dangerous to me ;).

Honza

--
Jan Kara <ja...@suse.com>
SUSE Labs, CR

[Tetsuo Handa]

On 2022/07/14 23:18, Jan Kara wrote:
> Hello,
>
> so this lockdep report looks real but is more related to OOM handling than
> to ext4 as such. The immediate problem I can see is that
> mem_cgroup_print_oom_meminfo() which is called under oom_lock calls
> memory_stat_format() which does GFP_KERNEL allocations to allocate buffers
> for dumping of MM statistics. This creates oom_lock -> fs reclaim
> dependency and because OOM can be hit (and thus oom_lock acquired) in
> practically any allocation (regardless of GFP_NOFS) this has a potential of
> creating real deadlock cycles.
>
> So should mem_cgroup_print_oom_meminfo() be using
> memalloc_nofs_save/restore() to avoid such deadlocks? Or perhaps someone
> sees another solution? Generally allocating memory to report OOM looks a
> bit dangerous to me ;).
>
> Honza

I think mem_cgroup_print_oom_meminfo() should use GFP_ATOMIC, for it will fall into
infinite loop if kmalloc(GFP_NOFS) under oom_lock reached __alloc_pages_may_oom() path.

[Shakeel Butt]

On Fri, Jul 15, 2022 at 07:24:55AM +0900, Tetsuo Handa wrote:
> On 2022/07/14 23:18, Jan Kara wrote:
> > Hello,
> >
> > so this lockdep report looks real but is more related to OOM handling than
> > to ext4 as such. The immediate problem I can see is that
> > mem_cgroup_print_oom_meminfo() which is called under oom_lock calls
> > memory_stat_format() which does GFP_KERNEL allocations to allocate buffers
> > for dumping of MM statistics. This creates oom_lock -> fs reclaim
> > dependency and because OOM can be hit (and thus oom_lock acquired) in
> > practically any allocation (regardless of GFP_NOFS) this has a potential of
> > creating real deadlock cycles.
> >
> > So should mem_cgroup_print_oom_meminfo() be using
> > memalloc_nofs_save/restore() to avoid such deadlocks? Or perhaps someone
> > sees another solution? Generally allocating memory to report OOM looks a
> > bit dangerous to me ;).

mem_cgroup_print_oom_meminfo() is called only for memcg OOMs. So, the
situaion would be dangerous only if the system is also OOM at that time.

> >
> > Honza
>
> I think mem_cgroup_print_oom_meminfo() should use GFP_ATOMIC, for it will fall into
> infinite loop if kmalloc(GFP_NOFS) under oom_lock reached __alloc_pages_may_oom() path.

I would prefer GFP_NOWAIT. This is printing info for memcg OOMs and if
the system is low on memory then memcg OOMs has lower importance than
the system state.

[Tetsuo Handa]

On 2022/07/15 10:39, Shakeel Butt wrote:
>> I think mem_cgroup_print_oom_meminfo() should use GFP_ATOMIC, for it will fall into
>> infinite loop if kmalloc(GFP_NOFS) under oom_lock reached __alloc_pages_may_oom() path.
>
> I would prefer GFP_NOWAIT. This is printing info for memcg OOMs and if
> the system is low on memory then memcg OOMs has lower importance than
> the system state.

Since killing a process in some memcg likely helps solving global OOM state,
system OOM condition might not be reported when memory allocation by
mem_cgroup_print_oom_meminfo() caused system OOM condition.

Therefore, we don't need to discard output from memcg OOM condition.