linux-kernel - Re: [PATCH V2] writeback: Fix wakeup and logging timeouts for !DETECT_HUNG

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Message-ID: <zyla6hpdipy42mohwluccjda6msrykavxofcfeuf3rigoq24t5@72kmw2rza4fs>
Date: Tue, 3 Feb 2026 10:08:43 +0100
From: Jan Kara <jack@...e.cz>
To: Huacai Chen <chenhuacai@...ngson.cn>
Cc: Huacai Chen <chenhuacai@...nel.org>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
	linux-fsdevel@...r.kernel.org, Xuefeng Li <lixuefeng@...ngson.cn>, 
	Julian Sun <sunjunchao@...edance.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] writeback: Fix wakeup and logging timeouts for
 !DETECT_HUNG_TASK

On Tue 03-02-26 14:30:23, Huacai Chen wrote:
> Recent changes of fs-writeback cause such warnings if DETECT_HUNG_TASK
> is not enabled:
> 
> INFO: The task sync:1342 has been waiting for writeback completion for more than 1 seconds.
> 
> The reason is sysctl_hung_task_timeout_secs is 0 when DETECT_HUNG_TASK
> is not enabled, then it causes the warning message even if the writeback
> lasts for only one second.
> 
> So guard the wakeup and logging with "#ifdef CONFIG_DETECT_HUNG_TASK",
> so as to eliminate the warning messages.
> 
> Fixes: 1888635532fb ("writeback: Wake up waiting tasks when finishing the writeback of a chunk.")
> Fixes: d6e621590764 ("writeback: Add logging for slow writeback (exceeds sysctl_hung_task_timeout_secs)")
> Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>

Thanks! Looks good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
> V2: Disable wakeup and logging for !DETECT_HUNG_TASK.
> 
>  fs/fs-writeback.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 5444fc706ac7..bfe469fff97c 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -198,13 +198,15 @@ static void wb_queue_work(struct bdi_writeback *wb,
>  
>  static bool wb_wait_for_completion_cb(struct wb_completion *done)
>  {
> +#ifdef CONFIG_DETECT_HUNG_TASK
>  	unsigned long waited_secs = (jiffies - done->wait_start) / HZ;
>  
> -	done->progress_stamp = jiffies;
>  	if (waited_secs > sysctl_hung_task_timeout_secs)
>  		pr_info("INFO: The task %s:%d has been waiting for writeback "
>  			"completion for more than %lu seconds.",
>  			current->comm, current->pid, waited_secs);
> +#endif
> +	done->progress_stamp = jiffies;
>  
>  	return !atomic_read(&done->cnt);
>  }
> @@ -2029,11 +2031,13 @@ static long writeback_sb_inodes(struct super_block *sb,
>  		 */
>  		__writeback_single_inode(inode, &wbc);
>  
> +#ifdef CONFIG_DETECT_HUNG_TASK
>  		/* Report progress to inform the hung task detector of the progress. */
>  		if (work->done && work->done->progress_stamp &&
>  		   (jiffies - work->done->progress_stamp) > HZ *
>  		   sysctl_hung_task_timeout_secs / 2)
>  			wake_up_all(work->done->waitq);
> +#endif
>  
>  		wbc_detach_inode(&wbc);
>  		work->nr_pages -= write_chunk - wbc.nr_to_write;
> -- 
> 2.47.3
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR