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Re: [RFC][PATCH v4 1/2] printk: Make printk() completely async

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On (03/18/16 14:49), Byungchul Park wrote:
[..]
> > http://marc.info/?l=linux-kernel&m=145750373530161
> 
> I checked it now. Do you mean the wake_up_process() introduced in the new
> patch in console_unlock()? If so, I also think it does not make a deadlock,
> just can make a recursion in the worst case. I thought it was the
> wake_up_process() in up() which is eventually called from console_unlock().
> A deadlock can happen with the wake_up_proces() in up(). :-)

I'm not addressing already existing problems here. I'm trying to
minimise the impact of new code only.

[..]
> diff --git a/kernel/locking/spinlock_debug.c b/kernel/locking/spinlock_debug.c
> index fd24588..30559c6 100644
> --- a/kernel/locking/spinlock_debug.c
> +++ b/kernel/locking/spinlock_debug.c
> @@ -138,14 +138,25 @@ static void __spin_lock_debug(raw_spinlock_t *lock)
>  {
>  	u64 i;
>  	u64 loops = loops_per_jiffy * HZ;
> +	static raw_spinlock_t *suspected_lock = NULL;

this has no chances to survive on SMP systems that have spin_lockup-ed on at
least two different spin locks.

I'd really prefer not to mix-in spin_dump/printk recursion problems into this
patch set. it makes sense not to make printk recursion detection worse due to
newly added spin_locks to vprintk_emit(), but that's it. this patch set set is
fixing other things in the first place.

	-ss

>  	for (i = 0; i < loops; i++) {
>  		if (arch_spin_trylock(&lock->raw_lock))
>  			return;
>  		__delay(1);
>  	}
> -	/* lockup suspected: */
> -	spin_dump(lock, "lockup suspected");
> +
> +	/*
> +	 * When we suspect a lockup, it's good enough to inform it once for
> +	 * the same lock. Otherwise it could cause an infinite recursion if
> +	 * it's within printk().
> +	 */
> +	if (suspected_lock != lock) {
> +		suspected_lock = lock;
> +		/* lockup suspected: */
> +		spin_dump(lock, "lockup suspected");
> +		suspected_lock = NULL;
> +	}
>  #ifdef CONFIG_SMP
>  	trigger_all_cpu_backtrace();
>  #endif
> -- 
> 1.9.1
> 

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[RFC][PATCH v4 0/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-03-14 15:20 +0100
  [RFC][PATCH v4 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-03-14 15:20 +0100
    Re: [RFC][PATCH v4 1/2] printk: Make printk() completely async Jan Kara <jack@suse.cz> - 2016-03-15 11:10 +0100
      Re: [RFC][PATCH v4 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-03-15 15:20 +0100
        Re: [RFC][PATCH v4 1/2] printk: Make printk() completely async Byungchul Park <byungchul.park@lge.com> - 2016-03-16 06:50 +0100
          Re: [RFC][PATCH v4 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-16 08:00 +0100
            Re: [RFC][PATCH v4 1/2] printk: Make printk() completely async Byungchul Park <byungchul.park@lge.com> - 2016-03-16 08:40 +0100
              Re: [RFC][PATCH v4 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-16 09:00 +0100
                Re: [RFC][PATCH v4 1/2] printk: Make printk() completely async Byungchul Park <byungchul.park@lge.com> - 2016-03-16 11:40 +0100
                Re: [RFC][PATCH v4 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-17 01:40 +0100
                Re: [RFC][PATCH v4 1/2] printk: Make printk() completely async Byungchul Park <byungchul.park@lge.com> - 2016-03-18 06:50 +0100
                Re: [RFC][PATCH v4 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-18 08:20 +0100
                RE: [RFC][PATCH v4 1/2] printk: Make printk() completely async "byungchul.park" <byungchul.park@lge.com> - 2016-03-18 09:30 +0100
          Re: [RFC][PATCH v4 1/2] printk: Make printk() completely async Byungchul Park <byungchul.park@lge.com> - 2016-03-16 08:10 +0100
            Re: [RFC][PATCH v4 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-16 08:10 +0100
    Re: [RFC][PATCH v4 1/2] printk: Make printk() completely async Petr Mladek <pmladek@suse.com> - 2016-03-15 17:00 +0100
      Re: [RFC][PATCH v4 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-16 03:10 +0100
        Re: [RFC][PATCH v4 1/2] printk: Make printk() completely async Byungchul Park <byungchul.park@lge.com> - 2016-03-16 03:20 +0100
          Re: [RFC][PATCH v4 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-16 03:40 +0100
  [RFC][PATCH v4 2/2] printk: Skip messages on oops Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-03-14 15:20 +0100
    Re: [RFC][PATCH v4 2/2] printk: Skip messages on oops Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-17 12:00 +0100

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