linux-kernel - Re: [RFC PATCH 1/2] smp: Reduce logging due to dump

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Date:   Fri, 28 Apr 2023 10:57:56 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Imran Khan <imran.f.khan@...cle.com>
Cc:     peterz@...radead.org, jgross@...e.com, vschneid@...hat.com,
        yury.norov@...il.com, tglx@...utronix.de,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] smp: Reduce logging due to dump_stack of CSD
 waiters.

On Sat, Apr 29, 2023 at 03:00:05AM +1000, Imran Khan wrote:
> If a waiter is waiting for CSD lock, its call stack will not change
> between first and subsequent hang detection for the same CSD lock.
> So dump_stack for the waiter only for first time detection.
> 
> This avoids excessive logging on large scale systems(with hundreds
> of CPUs) where repetitive dump_stack from hundreds of CPUs can flood
> the console.
> 
> Signed-off-by: Imran Khan <imran.f.khan@...cle.com>

Reviewed-by: Paul E. McKenney <paulmck@...nel.org>

> ---
>  kernel/smp.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/smp.c b/kernel/smp.c
> index ab3e5dad6cfe9..b7ccba677a0a0 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -248,7 +248,8 @@ static bool csd_lock_wait_toolong(struct __call_single_data *csd, u64 ts0, u64 *
>  			arch_send_call_function_single_ipi(cpu);
>  		}
>  	}
> -	dump_stack();
> +	if (firsttime)
> +		dump_stack();
>  	*ts1 = ts2;
>  
>  	return false;
> -- 
> 2.34.1
>