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From: Ingo Molnar <mingo@kernel.org>
To: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Vince Weaver <vincent.weaver@maine.edu>,
	linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Stephane Eranian <eranian@gmail.com>,
	"Paul E. McKenney" <paulmck@us.ibm.com>
Subject: Re: perf: aux area related crash and warnings
Date: Thu, 18 Jun 2015 11:09:55 +0200	[thread overview]
Message-ID: <20150618090954.GB22009@gmail.com> (raw)
In-Reply-To: <87381rg9zx.fsf@ashishki-desk.ger.corp.intel.com>


* Alexander Shishkin <alexander.shishkin@linux.intel.com> wrote:

> +void rb_free_aux(struct ring_buffer *rb)
> +{
> +	/*
> +	 * hold rb::refcount to make sure rb doesn't disappear
> +	 * before aux pages are freed
> +	 */
> +	if (WARN_ON_ONCE(!atomic_inc_not_zero(&rb->refcount)))
> +		return;
> +
> +	if (atomic_dec_and_test(&rb->aux_refcount))
> +		call_rcu(&rb->rcu_head, rb_free_rcu);
> +	else
> +		ring_buffer_put(rb);	/* matches the increment above */

Is call_rcu() NMI-safe? I don't think so ...

I think the life time rules of this object are really messed up if they can be 
freed from any fast path. How come the freeing can happen in NMI context? 
Shouldn't the hardware first stop, then we can free things from the system call 
path, or so?

Thanks,

	Ingo

next prev parent reply	other threads:[~2015-06-18  9:10 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-06-12  3:15 perf: aux area related crash and warnings Vince Weaver
2015-06-12 18:42 ` Vince Weaver
2015-06-15 12:20   ` Peter Zijlstra
2015-06-15 12:49     ` Alexander Shishkin
2015-06-15 20:24       ` Ingo Molnar
2015-06-16 11:37       ` Alexander Shishkin
2015-06-18  9:09         ` Ingo Molnar [this message]
2015-06-18  9:35           ` Alexander Shishkin
2015-06-18 10:24             ` Peter Zijlstra
2015-06-18 16:30           ` Paul E. McKenney
2015-06-18 10:32         ` Peter Zijlstra
2015-06-18 13:11           ` Alexander Shishkin
2015-06-19 14:21           ` Vince Weaver
2015-07-06 15:34           ` [tip:perf/urgent] perf: Fix AUX buffer refcounting tip-bot for Peter Zijlstra

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