linux-kernel - Re: [PATCH V3] writeback: Fix wakeup and logging timeouts for !DETECT_HUNG

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <paqvsxwf3v5hi7gwylfez4yddlswsem27hzqy37mxuapn7dxss@5vefpyohwlba>
Date: Tue, 3 Feb 2026 11:06:30 +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 V3] writeback: Fix wakeup and logging timeouts for
 !DETECT_HUNG_TASK

On Tue 03-02-26 17:40:14, 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.
> 
> Guard the wakeup and logging with "#ifdef CONFIG_DETECT_HUNG_TASK" can
> eliminate the warning messages. But on the other hand, it is possible
> that sysctl_hung_task_timeout_secs be also 0 when DETECT_HUNG_TASK is
> enabled. So let's just check the value of sysctl_hung_task_timeout_secs
> to decide whether do wakeup and logging.
> 
> 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>

Looks good. Feel free to add:

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

> ---
> V2: Disable wakeup and logging for !DETECT_HUNG_TASK.
> V3: Also handle the case for DETECT_HUNG_TASK if sysctl_hung_task_timeout_secs is 0.

Good catch!

								Honza

> 
>  fs/fs-writeback.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 5444fc706ac7..79b02ac66ac6 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -198,10 +198,11 @@ static void wb_queue_work(struct bdi_writeback *wb,
>  
>  static bool wb_wait_for_completion_cb(struct wb_completion *done)
>  {
> +	unsigned long timeout = sysctl_hung_task_timeout_secs;
>  	unsigned long waited_secs = (jiffies - done->wait_start) / HZ;
>  
>  	done->progress_stamp = jiffies;
> -	if (waited_secs > sysctl_hung_task_timeout_secs)
> +	if (timeout && (waited_secs > timeout))
>  		pr_info("INFO: The task %s:%d has been waiting for writeback "
>  			"completion for more than %lu seconds.",
>  			current->comm, current->pid, waited_secs);
> @@ -1944,6 +1945,7 @@ static long writeback_sb_inodes(struct super_block *sb,
>  		.range_end		= LLONG_MAX,
>  	};
>  	unsigned long start_time = jiffies;
> +	unsigned long timeout = sysctl_hung_task_timeout_secs;
>  	long write_chunk;
>  	long total_wrote = 0;  /* count both pages and inodes */
>  	unsigned long dirtied_before = jiffies;
> @@ -2030,9 +2032,8 @@ static long writeback_sb_inodes(struct super_block *sb,
>  		__writeback_single_inode(inode, &wbc);
>  
>  		/* 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)
> +		if (work->done && work->done->progress_stamp && timeout &&
> +		   (jiffies - work->done->progress_stamp) > HZ * timeout / 2)
>  			wake_up_all(work->done->waitq);
>  
>  		wbc_detach_inode(&wbc);
> -- 
> 2.47.3
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR