From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754906AbbFSR7N (ORCPT ); Fri, 19 Jun 2015 13:59:13 -0400 Received: from terminus.zytor.com ([198.137.202.10]:49134 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753462AbbFSR6s (ORCPT ); Fri, 19 Jun 2015 13:58:48 -0400 Date: Fri, 19 Jun 2015 10:57:42 -0700 From: tip-bot for Oleg Nesterov Message-ID: Cc: paulmck@linux.vnet.ibm.com, bp@alien8.de, brgerst@gmail.com, mingo@kernel.org, luto@amacapital.net, hpa@zytor.com, alexander.shishkin@linux.intel.com, oleg@redhat.com, akpm@linux-foundation.org, peterz@infradead.org, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, dvlasenk@redhat.com, tglx@linutronix.de Reply-To: bp@alien8.de, brgerst@gmail.com, mingo@kernel.org, paulmck@linux.vnet.ibm.com, luto@amacapital.net, alexander.shishkin@linux.intel.com, oleg@redhat.com, hpa@zytor.com, peterz@infradead.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, tglx@linutronix.de, dvlasenk@redhat.com, torvalds@linux-foundation.org In-Reply-To: <20150530200425.GA15748@redhat.com> References: <20150530200425.GA15748@redhat.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:perf/urgent] perf: Fix ring_buffer_attach() RCU sync, again Git-Commit-ID: 2f993cf093643b98477c421fa2b9a98dcc940323 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 2f993cf093643b98477c421fa2b9a98dcc940323 Gitweb: http://git.kernel.org/tip/2f993cf093643b98477c421fa2b9a98dcc940323 Author: Oleg Nesterov AuthorDate: Sat, 30 May 2015 22:04:25 +0200 Committer: Ingo Molnar CommitDate: Fri, 19 Jun 2015 09:38:45 +0200 perf: Fix ring_buffer_attach() RCU sync, again While looking for other users of get_state/cond_sync. I Found ring_buffer_attach() and it looks obviously buggy? Don't we need to ensure that we have "synchronize" _between_ list_del() and list_add() ? IOW. Suppose that ring_buffer_attach() preempts right_after get_state_synchronize_rcu() and gp completes before spin_lock(). In this case cond_synchronize_rcu() does nothing and we reuse ->rb_entry without waiting for gp in between? It also moves the ->rcu_pending check under "if (rb)", to make it more readable imo. Signed-off-by: Oleg Nesterov Signed-off-by: Peter Zijlstra (Intel) Cc: Alexander Shishkin Cc: Andrew Morton Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: dave@stgolabs.net Cc: der.herr@hofr.at Cc: josh@joshtriplett.org Cc: tj@kernel.org Fixes: b69cf53640da ("perf: Fix a race between ring_buffer_detach() and ring_buffer_attach()") Link: http://lkml.kernel.org/r/20150530200425.GA15748@redhat.com Signed-off-by: Ingo Molnar --- kernel/events/core.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index eddf1ed..0ceb386 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -4331,20 +4331,20 @@ static void ring_buffer_attach(struct perf_event *event, WARN_ON_ONCE(event->rcu_pending); old_rb = event->rb; - event->rcu_batches = get_state_synchronize_rcu(); - event->rcu_pending = 1; - spin_lock_irqsave(&old_rb->event_lock, flags); list_del_rcu(&event->rb_entry); spin_unlock_irqrestore(&old_rb->event_lock, flags); - } - if (event->rcu_pending && rb) { - cond_synchronize_rcu(event->rcu_batches); - event->rcu_pending = 0; + event->rcu_batches = get_state_synchronize_rcu(); + event->rcu_pending = 1; } if (rb) { + if (event->rcu_pending) { + cond_synchronize_rcu(event->rcu_batches); + event->rcu_pending = 0; + } + spin_lock_irqsave(&rb->event_lock, flags); list_add_rcu(&event->rb_entry, &rb->event_list); spin_unlock_irqrestore(&rb->event_lock, flags); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/