Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750750AbWHTLov (ORCPT ); Sun, 20 Aug 2006 07:44:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750751AbWHTLov (ORCPT ); Sun, 20 Aug 2006 07:44:51 -0400 Received: from filfla-vlan276.msk.corbina.net ([213.234.233.49]:59362 "EHLO screens.ru") by vger.kernel.org with ESMTP id S1750750AbWHTLou (ORCPT ); Sun, 20 Aug 2006 07:44:50 -0400 Date: Sun, 20 Aug 2006 20:08:52 +0400 From: Oleg Nesterov To: Jens Axboe Cc: Andrew Morton , "Paul E. McKenney" , linux-kernel@vger.kernel.org Subject: [PATCH] fix? current_io_context() vs set_task_ioprio() race Message-ID: <20060820160852.GA2186@oleg> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1411 Lines: 37 I know nothing about io scheduler, but I suspect set_task_ioprio() is not safe. current_io_context() initializes "struct io_context", then sets ->io_context. set_task_ioprio() running on another cpu may see the changes out of order, so ->set_ioprio(ioc) may use io_context which was not initialized properly. Signed-off-by: Oleg Nesterov --- 2.6.18-rc4/block/ll_rw_blk.c~3_race 2006-07-16 01:53:08.000000000 +0400 +++ 2.6.18-rc4/block/ll_rw_blk.c 2006-08-20 19:30:10.000000000 +0400 @@ -3628,6 +3628,8 @@ struct io_context *current_io_context(gf ret->nr_batch_requests = 0; /* because this is 0 */ ret->aic = NULL; ret->cic_root.rb_node = NULL; + /* make sure set_task_ioprio() sees the settings above */ + smp_wmb(); tsk->io_context = ret; } --- 2.6.18-rc4/fs/ioprio.c~3_race 2006-08-20 19:09:08.000000000 +0400 +++ 2.6.18-rc4/fs/ioprio.c 2006-08-20 19:57:14.000000000 +0400 @@ -44,6 +44,9 @@ static int set_task_ioprio(struct task_s task->ioprio = ioprio; ioc = task->io_context; + /* see wmb() in current_io_context() */ + smp_read_barrier_depends(); + if (ioc && ioc->set_ioprio) ioc->set_ioprio(ioc, ioprio); - 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/