linux-kernel - Re: [PATCH] zap_pid_ns_processes: clear TIF_NOTIFY_SIGNAL along with TIF

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Date: Sat, 8 Jun 2024 10:00:36 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Rachel Menge <rachelmenge@...ux.microsoft.com>,
	linux-kernel@...r.kernel.org, rcu@...r.kernel.org,
	Wei Fu <fuweid89@...il.com>, apais@...ux.microsoft.com,
	Sudhanva Huruli <Sudhanva.Huruli@...rosoft.com>,
	Jens Axboe <axboe@...nel.dk>,
	Christian Brauner <brauner@...nel.org>,
	Mike Christie <michael.christie@...cle.com>,
	Joel Granados <j.granados@...sung.com>,
	Mateusz Guzik <mjguzik@...il.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>
Subject: Re: [PATCH] zap_pid_ns_processes: clear TIF_NOTIFY_SIGNAL along with
 TIF_SIGPENDING

On Sat, Jun 08, 2024 at 02:06:16PM +0200, Oleg Nesterov wrote:
> kernel_wait4() doesn't sleep and returns -EINTR if there is no
> eligible child and signal_pending() is true.
> 
> That is why zap_pid_ns_processes() clears TIF_SIGPENDING but this is not
> enough, it should also clear TIF_NOTIFY_SIGNAL to make signal_pending()
> return false and avoid a busy-wait loop.
> 
> Fixes: 12db8b690010 ("entry: Add support for TIF_NOTIFY_SIGNAL")
> Reported-by: Rachel Menge <rachelmenge@...ux.microsoft.com>
> Closes: https://lore.kernel.org/all/1386cd49-36d0-4a5c-85e9-bc42056a5a38@linux.microsoft.com/
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Reviewed-by: Boqun Feng <boqun.feng@...il.com>

Wei, appreciate it if you could share some test result and provide a
Tested-by tag. Thanks!

Regards,
Boqun

> ---
>  kernel/pid_namespace.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index dc48fecfa1dc..25f3cf679b35 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -218,6 +218,7 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
>  	 */
>  	do {
>  		clear_thread_flag(TIF_SIGPENDING);
> +		clear_thread_flag(TIF_NOTIFY_SIGNAL);
>  		rc = kernel_wait4(-1, NULL, __WALL, NULL);
>  	} while (rc != -ECHILD);
>  
> -- 
> 2.25.1.362.g51ebf55
> 
>