linux-kernel - Re: [PATCH 2/3] locking/csd_lock: Provide an indication of ongoing CSD-lock stall

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Message-ID: <ee33a2c3e32d98b5fc04983745c47f918f9ea2d2.camel@surriel.com>
Date: Sat, 13 Jul 2024 13:16:47 -0400
From: Rik van Riel <riel@...riel.com>
To: neeraj.upadhyay@...nel.org, linux-kernel@...r.kernel.org
Cc: rcu@...r.kernel.org, kernel-team@...a.com, rostedt@...dmis.org, 
 mingo@...nel.org, peterz@...radead.org, paulmck@...nel.org,
 leobras@...hat.com,  imran.f.khan@...cle.com
Subject: Re: [PATCH  2/3] locking/csd_lock: Provide an indication of ongoing
 CSD-lock stall

On Sat, 2024-07-13 at 22:28 +0530, neeraj.upadhyay@...nel.org wrote:
> 
> @@ -228,6 +241,7 @@ static bool
> csd_lock_wait_toolong(call_single_data_t *csd, u64 ts0, u64 *ts1, in
>  		cpu = csd_lock_wait_getcpu(csd);
>  		pr_alert("csd: CSD lock (#%d) got unstuck on
> CPU#%02d, CPU#%02d released the lock.\n",
>  			 *bug_id, raw_smp_processor_id(), cpu);
> +		atomic_dec(&n_csd_lock_stuck);
>  		return true;
>  	}
>  

So we decrement it when it gets unstuck. Good.

> @@ -251,6 +265,8 @@ static bool
> csd_lock_wait_toolong(call_single_data_t *csd, u64 ts0, u64 *ts1, in
>  	pr_alert("csd: %s non-responsive CSD lock (#%d) on CPU#%d,
> waiting %lld ns for CPU#%02d %pS(%ps).\n",
>  		 firsttime ? "Detected" : "Continued", *bug_id,
> raw_smp_processor_id(), (s64)ts_delta,
>  		 cpu, csd->func, csd->info);
> +	if (firsttime)
> +		atomic_dec(&n_csd_lock_stuck);
> 

However, I don't see any place where it is incremented when things
get stuck, and this line decrements it when a CPU gets stuck for
the first time?

Should this be an atomic_inc?

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