Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754239AbbFRJKI (ORCPT ); Thu, 18 Jun 2015 05:10:08 -0400 Received: from mail-wi0-f169.google.com ([209.85.212.169]:34327 "EHLO mail-wi0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753230AbbFRJJ7 (ORCPT ); Thu, 18 Jun 2015 05:09:59 -0400 Date: Thu, 18 Jun 2015 11:09:55 +0200 From: Ingo Molnar To: Alexander Shishkin Cc: Peter Zijlstra , Vince Weaver , linux-kernel@vger.kernel.org, Ingo Molnar , Arnaldo Carvalho de Melo , Stephane Eranian , "Paul E. McKenney" Subject: Re: perf: aux area related crash and warnings Message-ID: <20150618090954.GB22009@gmail.com> References: <20150615122054.GY3644@twins.programming.kicks-ass.net> <87egld2l2o.fsf@ashishki-desk.ger.corp.intel.com> <87381rg9zx.fsf@ashishki-desk.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87381rg9zx.fsf@ashishki-desk.ger.corp.intel.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1017 Lines: 32 * Alexander Shishkin 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/