Re: [RFC V2 PATCH 3/3] timer: warn when del_timer_sync() used in hardirq context

[Oleg Nesterov <oleg@redhat.com>]

On 08/25, Yong Zhang wrote:
>
> From: Yong Zhang <yong.zhang@windriver.com>
>
> Add explict warning to prevent del_timer_sync() from using
> in hardirq context.

Agreed, del_timer_sync() from softirq should be OK.

> Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Ingo Molnar <mingo@elte.hu>
> ---
>  kernel/timer.c |    6 +++++-
>  1 files changed, 5 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/timer.c b/kernel/timer.c
> index 08c9559..1bc4b4a 100644
> --- a/kernel/timer.c
> +++ b/kernel/timer.c
> @@ -996,7 +996,11 @@ int del_timer_sync(struct timer_list *timer)
>  	lock_map_release(&timer->lockdep_map);
>  	local_bh_enable();
>  #endif
> -
> +	/*
> +	 * don't use it in hardirq context, because it
> +	 * could lead to deadlock.
> +	 */
> +	WARN_ON(in_irq());
>  	for (;;) {
>  		int ret = try_to_del_timer_sync(timer);
>  		if (ret >= 0)
> -- 
> 1.7.0.4
>