From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752669AbaFEPbH (ORCPT ); Thu, 5 Jun 2014 11:31:07 -0400 Received: from mail-ie0-f174.google.com ([209.85.223.174]:52378 "EHLO mail-ie0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752307AbaFEPbE (ORCPT ); Thu, 5 Jun 2014 11:31:04 -0400 From: Trond Myklebust To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, John Stultz , Ingo Molnar , "David S. Miller" , Al Viro Subject: [PATCH] Revert lockdep check in raw_seqcount_begin Date: Thu, 5 Jun 2014 11:31:01 -0400 Message-Id: <1401982261-11246-1-git-send-email-trond.myklebust@primarydata.com> X-Mailer: git-send-email 1.9.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This commit reverts the addition of lockdep checking to raw_seqcount_begin for the following reasons: 1) It violates the naming convention that raw_* functions should not do lockdep checks (a convention that is also followed by the other raw_*_seqcount_begin functions). 2) raw_seqcount_begin does not spin, so it can only be part of an ABBA deadlock in very special circumstances (for instance if a lock is held across the entire raw_seqcount_begin()+read_seqcount_retry() loop while also being taken inside the write_seqcount protected area). 3) It is causing false positives with some existing callers, and there is no non-lockdep alternative for those callers to use. None of the three existing callers (__d_lookup_rcu, netdev_get_name, and the NFS state code) appear to use the function in a manner that is ABBA deadlock prone. Fixes: 1ca7d67cf5d5: seqcount: Add lockdep functionality to seqcount/seqlock Cc: John Stultz Cc: Peter Zijlstra Cc: Ingo Molnar Cc: "David S. Miller" Cc: Al Viro Link: http://lkml.kernel.org/r/CAHQdGtRR6SvEhXiqWo24hoUh9AU9cL82Z8Z-d8-7u951F_d+5g@mail.gmail.com Signed-off-by: Trond Myklebust --- include/linux/seqlock.h | 2 -- 1 file changed, 2 deletions(-) diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h index 535f158977b9..8cf350325dc6 100644 --- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -164,8 +164,6 @@ static inline unsigned read_seqcount_begin(const seqcount_t *s) static inline unsigned raw_seqcount_begin(const seqcount_t *s) { unsigned ret = ACCESS_ONCE(s->sequence); - - seqcount_lockdep_reader_access(s); smp_rmb(); return ret & ~1; } -- 1.9.3