linux-kernel - Re: [patch 20/45] signal: Replace BUG

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Date:   Tue, 4 Jul 2023 12:24:06 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>,
        John Stultz <jstultz@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [patch 20/45] signal: Replace BUG_ON()s

On Tue, Jun 06, 2023 at 04:37:50PM +0200, Thomas Gleixner wrote:
> These really can be handled gracefully without killing the machine.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  kernel/signal.c |   11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -1932,10 +1932,11 @@ struct sigqueue *sigqueue_alloc(void)
>  
>  void sigqueue_free(struct sigqueue *q)
>  {
> -	unsigned long flags;
>  	spinlock_t *lock = &current->sighand->siglock;
> +	unsigned long flags;
>  
> -	BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));
> +	if (WARN_ON_ONCE(!(q->flags & SIGQUEUE_PREALLOC)))
> +		return;
>  	/*
>  	 * We must hold ->siglock while testing q->list
>  	 * to serialize with collect_signal() or with
> @@ -1963,7 +1964,10 @@ int send_sigqueue(struct sigqueue *q, st
>  	unsigned long flags;
>  	int ret, result;
>  
> -	BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));
> +	if (WARN_ON_ONCE(!(q->flags & SIGQUEUE_PREALLOC)))
> +		return 0;
> +	if (WARN_ON_ONCE(q->info.si_code != SI_TIMER))
> +		return 0;

Previously it only forbid _requeuing_ other things than posix timers.
Now it only allows posix timers at all.

But anyway posix timers is the only user so far:

Reviewed-by: Frederic Weisbecker <frederic@...nel.org>


>  
>  	ret = -1;
>  	rcu_read_lock();
> @@ -1998,7 +2002,6 @@ int send_sigqueue(struct sigqueue *q, st
>  		 * If an SI_TIMER entry is already queue just increment
>  		 * the overrun count.
>  		 */
> -		BUG_ON(q->info.si_code != SI_TIMER);
>  		q->info.si_overrun++;
>  		result = TRACE_SIGNAL_ALREADY_PENDING;
>  		goto out;
>