Re: [PATCH] writeback: Fix wakeup and logging timeouts for !DETECT_HUNG_TASK

[Julian Sun <sunjunchao@bytedance.com>]

On 1/31/26 5:07 PM, 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.
> 
> I believe the wakeup and logging is also useful for !DETECT_HUNG_TASK,
> so I don't want to disable them completely. As DEFAULT_HUNG_TASK_TIMEOUT
> is 120 seconds, so for the !DETECT_HUNG_TASK case let's use 120 seconds
> instead of sysctl_hung_task_timeout_secs.
> 
> 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@loongson.cn>
> ---
>   fs/fs-writeback.c | 15 ++++++++++++---
>   1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 5444fc706ac7..847e46f0e019 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -198,10 +198,15 @@ static void wb_queue_work(struct bdi_writeback *wb,
>   
>   static bool wb_wait_for_completion_cb(struct wb_completion *done)
>   {
> +#ifndef CONFIG_DETECT_HUNG_TASK
> +	unsigned long hung_secs = 120;
> +#else
> +	unsigned long hung_secs = sysctl_hung_task_timeout_secs;
> +#endif
>   	unsigned long waited_secs = (jiffies - done->wait_start) / HZ;
>   
>   	done->progress_stamp = jiffies;
> -	if (waited_secs > sysctl_hung_task_timeout_secs)
> +	if (waited_secs > hung_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);
> @@ -1947,6 +1952,11 @@ static long writeback_sb_inodes(struct super_block *sb,
>   	long write_chunk;
>   	long total_wrote = 0;  /* count both pages and inodes */
>   	unsigned long dirtied_before = jiffies;
> +#ifndef CONFIG_DETECT_HUNG_TASK
> +	unsigned long hung_secs = 120;
> +#else
> +	unsigned long hung_secs = sysctl_hung_task_timeout_secs;
> +#endif
>   
>   	if (work->for_kupdate)
>   		dirtied_before = jiffies -
> @@ -2031,8 +2041,7 @@ static long writeback_sb_inodes(struct super_block *sb,
>   
>   		/* 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)
> +		   (jiffies - work->done->progress_stamp) > HZ * hung_secs / 2)
>   			wake_up_all(work->done->waitq);
>   
>   		wbc_detach_inode(&wbc);

Thanks for the patch, looks good to me.

Reviewed-by: Julian Sun <sunjunchao@bytedance.com>


-- 
Julian Sun <sunjunchao@bytedance.com>