linux-kernel - Re: [PATCH] fs: quota: create dedicated workqueue for quota_release

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Message-ID: <49611228-50a8-416b-ac3d-d8b2869c2fe1@samsung.com>
Date: Wed, 3 Sep 2025 14:01:46 +0530
From: Shashank A P <shashank.ap@...sung.com>
To: Jan Kara <jack@...e.cz>
Cc: jack@...e.com, linux-kernel@...r.kernel.org, shadakshar.i@...sung.com,
	thiagu.r@...sung.com, hy50.seo@...sung.com, kwangwon.min@...sung.com,
	alim.akhtar@...sung.com, h10.kim@...sung.com, kwmad.kim@...sung.com,
	selvarasu.g@...sung.com, stable@...r.kernel.org
Subject: Re: [PATCH] fs: quota: create dedicated workqueue for
 quota_release_work


On 9/2/2025 7:17 PM, Jan Kara wrote:
> On Mon 01-09-25 14:59:00, Shashank A P wrote:
>> There is a kernel panic due to WARN_ONCE when panic_on_warn is set.
>>
>> This issue occurs when writeback is triggered due to sync call for an
>> opened file(ie, writeback reason is WB_REASON_SYNC). When f2fs balance
>> is needed at sync path, flush for quota_release_work is triggered.
>> By default quota_release_work is queued to "events_unbound" queue which
>> does not have WQ_MEM_RECLAIM flag. During f2fs balance "writeback"
>> workqueue tries to flush quota_release_work causing kernel panic due to
>> MEM_RECLAIM flag mismatch errors.
>>
>> This patch creates dedicated workqueue with WQ_MEM_RECLAIM flag
>> for work quota_release_work.
>>
>> ------------[ cut here ]------------
>> WARNING: CPU: 4 PID: 14867 at kernel/workqueue.c:3721 check_flush_dependency+0x13c/0x148
>> Call trace:
>>   check_flush_dependency+0x13c/0x148
>>   __flush_work+0xd0/0x398
>>   flush_delayed_work+0x44/0x5c
>>   dquot_writeback_dquots+0x54/0x318
>>   f2fs_do_quota_sync+0xb8/0x1a8
>>   f2fs_write_checkpoint+0x3cc/0x99c
>>   f2fs_gc+0x190/0x750
>>   f2fs_balance_fs+0x110/0x168
>>   f2fs_write_single_data_page+0x474/0x7dc
>>   f2fs_write_data_pages+0x7d0/0xd0c
>>   do_writepages+0xe0/0x2f4
>>   __writeback_single_inode+0x44/0x4ac
>>   writeback_sb_inodes+0x30c/0x538
>>   wb_writeback+0xf4/0x440
>>   wb_workfn+0x128/0x5d4
>>   process_scheduled_works+0x1c4/0x45c
>>   worker_thread+0x32c/0x3e8
>>   kthread+0x11c/0x1b0
>>   ret_from_fork+0x10/0x20
>> Kernel panic - not syncing: kernel: panic_on_warn set ...
>>
>> Fixes: ac6f420291b3 ("quota: flush quota_release_work upon quota writeback")
>> CC: stable@...r.kernel.org
>> Signed-off-by: Shashank A P <shashank.ap@...sung.com>
> Thanks. It seems a bit unfortunate that we have to create a separate
> workqueue just for this but I don't see a different easy solution. So I've
> added your patch to my tree.
>
> 								Honza

Hi Jan Kara,
Thanks for your comments.

We've got a below kernel warning from kernel test 
robot(lkp@...el.com)that related to the changes, and we need your 
suggestions to resolve this warning as its merged already in your tree.

Should we post a new patch version to fix this warning, or can you 
please incorporate the fix while applying it to linux-next?


sparse warnings: (new ones prefixed by >>)
 >> fs/quota/dquot.c:166:25: sparse: sparse: symbol 'quota_unbound_wq' 
was not declared. Should it be static?

https://lore.kernel.org/all/202509031153.0ACADDn6-lkp@intel.com/

Thanks,
Shashank

>
>> ---
>>   fs/quota/dquot.c | 10 +++++++++-
>>   1 file changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
>> index df4a9b348769..d0f83a0c42df 100644
>> --- a/fs/quota/dquot.c
>> +++ b/fs/quota/dquot.c
>> @@ -162,6 +162,9 @@ static struct quota_module_name module_names[] = INIT_QUOTA_MODULE_NAMES;
>>   /* SLAB cache for dquot structures */
>>   static struct kmem_cache *dquot_cachep;
>>   
>> +/* workqueue for work quota_release_work*/
>> +struct workqueue_struct *quota_unbound_wq;
>> +
>>   void register_quota_format(struct quota_format_type *fmt)
>>   {
>>   	spin_lock(&dq_list_lock);
>> @@ -881,7 +884,7 @@ void dqput(struct dquot *dquot)
>>   	put_releasing_dquots(dquot);
>>   	atomic_dec(&dquot->dq_count);
>>   	spin_unlock(&dq_list_lock);
>> -	queue_delayed_work(system_unbound_wq, &quota_release_work, 1);
>> +	queue_delayed_work(quota_unbound_wq, &quota_release_work, 1);
>>   }
>>   EXPORT_SYMBOL(dqput);
>>   
>> @@ -3041,6 +3044,11 @@ static int __init dquot_init(void)
>>   
>>   	shrinker_register(dqcache_shrinker);
>>   
>> +	quota_unbound_wq = alloc_workqueue("quota_events_unbound",
>> +					   WQ_UNBOUND | WQ_MEM_RECLAIM, WQ_MAX_ACTIVE);
>> +	if (!quota_unbound_wq)
>> +		panic("Cannot create quota_unbound_wq\n");
>> +
>>   	return 0;
>>   }
>>   fs_initcall(dquot_init);
>> -- 
>> 2.34.1
>>