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

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Message-ID: <vpv4mxr565y5ykjvqntl6ke43sojcuqfc74ai5bfs6zg7e6qze@3qlidrkuvn22>
Date: Wed, 3 Sep 2025 12:37:20 +0200
From: Jan Kara <jack@...e.cz>
To: Shashank A P <shashank.ap@...sung.com>
Cc: Jan Kara <jack@...e.cz>, 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 Wed 03-09-25 14:01:46, Shashank A P wrote:
> 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 for noticing. Somehow I didn't get this notification. Anyway, I've
fixed up the commit in my tree to declare quota_unbound_wq as static.

								Honza

> >> ---
> >>   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
> >>
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR