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

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Message-ID: <ufb72d6p54cxyzcy5glrfzaz7xm3inzp44k6rdff5on3daua4s@u2rf7xt4hdie>
Date: Tue, 2 Sep 2025 15:47:18 +0200
From: Jan Kara <jack@...e.cz>
To: Shashank A P <shashank.ap@...sung.com>
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 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

> ---
>  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