From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp.codeaurora.org by pdx-caf-mail.web.codeaurora.org (Dovecot) with LMTP id HCTqOKhNGVvycgAAmS7hNA ; Thu, 07 Jun 2018 15:22:26 +0000 Received: by smtp.codeaurora.org (Postfix, from userid 1000) id 61B43607E7; Thu, 7 Jun 2018 15:22:26 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on pdx-caf-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI autolearn=ham autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by smtp.codeaurora.org (Postfix) with ESMTP id D89A1606DD; Thu, 7 Jun 2018 15:22:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org D89A1606DD Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=decadent.org.uk Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935756AbeFGPWX (ORCPT + 25 others); Thu, 7 Jun 2018 11:22:23 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:41241 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935494AbeFGO7A (ORCPT ); Thu, 7 Jun 2018 10:59:00 -0400 Received: from [148.252.241.226] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.84_2) (envelope-from ) id 1fQvbG-0005Zl-68; Thu, 07 Jun 2018 15:09:14 +0100 Received: from ben by deadeye with local (Exim 4.91) (envelope-from ) id 1fQvbC-0003FG-PG; Thu, 07 Jun 2018 15:09:10 +0100 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Oleg Nesterov" , "Benjamin LaHaise" Date: Thu, 07 Jun 2018 15:05:21 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 355/410] aio: kill the misleading rcu read locks in ioctx_add_table() and kill_ioctx() In-Reply-To: X-SA-Exim-Connect-IP: 148.252.241.226 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.57-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Oleg Nesterov commit 855ef0dec7271ff7be7381feaaf3f4aed80bd503 upstream. ioctx_add_table() is the writer, it does not need rcu_read_lock() to protect ->ioctx_table. It relies on mm->ioctx_lock and rcu locks just add the confusion. And it doesn't need rcu_dereference() by the same reason, it must see any updates previously done under the same ->ioctx_lock. We could use rcu_dereference_protected() but the patch uses rcu_dereference_raw(), the function is simple enough. The same for kill_ioctx(), although it does not update the pointer. Signed-off-by: Oleg Nesterov Signed-off-by: Benjamin LaHaise Signed-off-by: Ben Hutchings --- fs/aio.c | 14 +++----------- 1 file changed, 3 insertions(+), 11 deletions(-) --- a/fs/aio.c +++ b/fs/aio.c @@ -563,8 +563,7 @@ static int ioctx_add_table(struct kioctx struct aio_ring *ring; spin_lock(&mm->ioctx_lock); - rcu_read_lock(); - table = rcu_dereference(mm->ioctx_table); + table = rcu_dereference_raw(mm->ioctx_table); while (1) { if (table) @@ -572,7 +571,6 @@ static int ioctx_add_table(struct kioctx if (!table->table[i]) { ctx->id = i; table->table[i] = ctx; - rcu_read_unlock(); spin_unlock(&mm->ioctx_lock); /* While kioctx setup is in progress, @@ -586,8 +584,6 @@ static int ioctx_add_table(struct kioctx } new_nr = (table ? table->nr : 1) * 4; - - rcu_read_unlock(); spin_unlock(&mm->ioctx_lock); table = kzalloc(sizeof(*table) + sizeof(struct kioctx *) * @@ -598,8 +594,7 @@ static int ioctx_add_table(struct kioctx table->nr = new_nr; spin_lock(&mm->ioctx_lock); - rcu_read_lock(); - old = rcu_dereference(mm->ioctx_table); + old = rcu_dereference_raw(mm->ioctx_table); if (!old) { rcu_assign_pointer(mm->ioctx_table, table); @@ -749,12 +744,9 @@ static int kill_ioctx(struct mm_struct * spin_lock(&mm->ioctx_lock); - rcu_read_lock(); - table = rcu_dereference(mm->ioctx_table); - + table = rcu_dereference_raw(mm->ioctx_table); WARN_ON(ctx != table->table[ctx->id]); table->table[ctx->id] = NULL; - rcu_read_unlock(); spin_unlock(&mm->ioctx_lock); /* percpu_ref_kill() will do the necessary call_rcu() */