linux-kernel - Re: [PATCH] smp/call: Detect stuck CSD locks

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Message-ID: <20150403054708.GA12316@gmail.com>
Date:	Fri, 3 Apr 2015 07:47:08 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Chris J Arges <chris.j.arges@...onical.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rafael David Tinoco <inaddy@...ntu.com>,
	Peter Anvin <hpa@...or.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Gema Gomez <gema.gomez-solano@...onical.com>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH] smp/call: Detect stuck CSD locks


* Ingo Molnar <mingo@...nel.org> wrote:

> +static void csd_lock_wait(struct call_single_data *csd, int cpu)
>  {
> -	while (csd->flags & CSD_FLAG_LOCK)
> +	int bug_id = 0;
> +	u64 ts0, ts1, ts_delta;
> +
> +	ts0 = jiffies_to_msecs(jiffies);

Note that while 'jiffies' is a global variable, it's read-mostly 
accessed, so it is a pretty cheap way to acquire a timestamp in such a 
simple polling context that has irqs enabled.

Thanks,

	Ingo
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