From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753483AbcICG6f (ORCPT ); Sat, 3 Sep 2016 02:58:35 -0400 Received: from mga09.intel.com ([134.134.136.24]:36317 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752463AbcICG6d (ORCPT ); Sat, 3 Sep 2016 02:58:33 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.30,274,1470726000"; d="scan'208";a="1024552570" From: Felipe Balbi To: Peter Zijlstra , Alan Stern Cc: "Paul E. McKenney" , Ingo Molnar , USB list , Kernel development list Subject: Re: Memory barrier needed with wake_up_process()? In-Reply-To: <20160902221658.GO10153@twins.programming.kicks-ass.net> References: <20160902191857.GL10153@twins.programming.kicks-ass.net> <20160902221658.GO10153@twins.programming.kicks-ass.net> User-Agent: Notmuch/0.22.1+63~g994277e (https://notmuchmail.org) Emacs/25.1.1 (x86_64-pc-linux-gnu) Date: Sat, 03 Sep 2016 09:58:09 +0300 Message-ID: <8737lh79mm.fsf@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org hi, Peter Zijlstra writes: > On Fri, Sep 02, 2016 at 04:16:54PM -0400, Alan Stern wrote: >> Felipe, your tests will show whether my guess was totally off-base. >> For the new people, Felipe is tracking down a problem that involves >> exactly the code sequence listed at the top of the email, where we know >> that the wakeup routine runs but nevertheless the task sleeps. At >> least, that's what it looks like at the moment. > > What arch are you seeing this on? x86. Skylake to be exact. The following change survived through the night: diff --git a/drivers/usb/gadget/function/f_mass_storage.c b/drivers/usb/gadget/function/f_mass_storage.c index 8f3659b65f53..d31581dd5ce5 100644 --- a/drivers/usb/gadget/function/f_mass_storage.c +++ b/drivers/usb/gadget/function/f_mass_storage.c @@ -395,7 +395,7 @@ static int fsg_set_halt(struct fsg_dev *fsg, struct usb_ep *ep) /* Caller must hold fsg->lock */ static void wakeup_thread(struct fsg_common *common) { - smp_wmb(); /* ensure the write of bh->state is complete */ + smp_mb(); /* ensure the write of bh->state is complete */ /* Tell the main thread that something has happened */ common->thread_wakeup_needed = 1; if (common->thread_task) @@ -626,7 +626,7 @@ static int sleep_thread(struct fsg_common *common, bool can_freeze) } __set_current_state(TASK_RUNNING); common->thread_wakeup_needed = 0; - smp_rmb(); /* ensure the latest bh->state is visible */ + smp_mb(); /* ensure the latest bh->state is visible */ return rc; } I'll keep it running until Monday at least -- balbi