Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755066Ab3HBQaH (ORCPT ); Fri, 2 Aug 2013 12:30:07 -0400 Received: from mail-we0-f177.google.com ([74.125.82.177]:33696 "EHLO mail-we0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754798Ab3HBQaE (ORCPT ); Fri, 2 Aug 2013 12:30:04 -0400 From: Frederic Weisbecker To: Peter Zijlstra , Jiri Olsa Cc: LKML , Frederic Weisbecker , Ingo Molnar , Namhyung Kim , Arnaldo Carvalho de Melo , Stephane Eranian Subject: [PATCH 1/3] perf: Rollback callchain buffer refcount under the callchain mutex Date: Fri, 2 Aug 2013 18:29:54 +0200 Message-Id: <1375460996-16329-2-git-send-email-fweisbec@gmail.com> X-Mailer: git-send-email 1.7.5.4 In-Reply-To: <1375460996-16329-1-git-send-email-fweisbec@gmail.com> References: <1375460996-16329-1-git-send-email-fweisbec@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1683 Lines: 51 When we fail to allocate the callchain buffers, we rollback the refcount we did and return from get_callchain_buffers(). However we take the refcount and allocate under the callchain lock but the rollback is done outside the lock. As a result, while we rollback, some concurrent callchain user may call get_callchain_buffers(), see the non-zero refcount and give up because the buffers are NULL without itself retrying the allocation. The consequences aren't that bad but that behaviour looks weird enough and it's better to give their chances to the following callchain users where we failed. Reported-by: Jiri Olsa Signed-off-by: Frederic Weisbecker Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Jiri Olsa Cc: Namhyung Kim Cc: Arnaldo Carvalho de Melo Cc: Stephane Eranian --- kernel/events/callchain.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-) diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c index 76a8bc5..97b67df 100644 --- a/kernel/events/callchain.c +++ b/kernel/events/callchain.c @@ -116,10 +116,11 @@ int get_callchain_buffers(void) err = alloc_callchain_buffers(); exit: - mutex_unlock(&callchain_mutex); if (err) atomic_dec(&nr_callchain_events); + mutex_unlock(&callchain_mutex); + return err; } -- 1.7.5.4 -- 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/