From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: linux-nfs-owner@vger.kernel.org Received: from mail-gx0-f174.google.com ([209.85.161.174]:45588 "EHLO mail-gx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754864Ab1KAS17 (ORCPT ); Tue, 1 Nov 2011 14:27:59 -0400 Date: Tue, 1 Nov 2011 11:27:53 -0700 From: Tejun Heo To: Oleg Nesterov Cc: Jeff Layton , "Rafael J. Wysocki" , Steve French , linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, linux-cifs@vger.kernel.org, "J. Bruce Fields" , Neil Brown , trond.myklebust@netapp.com, linux-nfs@vger.kernel.org Subject: Re: [RFC PATCH] freezer: revert 27920651fe "PM / Freezer: Make fake_signal_wake_up() wake TASK_KILLABLE tasks too" Message-ID: <20111101182753.GW18855@google.com> References: <20111031221743.GA18855@google.com> <201111010024.16659.rjw@sisk.pl> <20111031233059.GI18855@google.com> <20111101005505.GO18855@google.com> <20111101041337.39077229@tlielax.poochiereds.net> <20111101065958.50addab5@tlielax.poochiereds.net> <20111101163059.GR18855@google.com> <20111101175953.GB5358@redhat.com> <20111101180601.GV18855@google.com> <20111101181329.GA6739@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20111101181329.GA6739@redhat.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: Hello, On Tue, Nov 01, 2011 at 07:13:29PM +0100, Oleg Nesterov wrote: > On 11/01, Tejun Heo wrote: > > > > Yeah yeah, Trond already pointed it out. I forgot about the > > sigpending special case in schedule(), which I think is rather odd, > > I disagree with "rather odd" ;) > > We have a lot of examples of > > current->state = TASK_INTERRUPTIBLE; > ... > if (signal_pending()) > break; > schedule(); > > Without that special case in schedule() the code above becomes racy. > Just consider __wait_event_interruptible(). But __wait_event_interruptible() does proper set-TASK_*, check sigpending and schedule() sequence. As long as the waker performs seg-sigpending, wakeup sequence in the correct order, nothing is broken (as w/ any other wakeup conditions). The special case deals with callers which don't check sigpending between set-TASK_* and schedule() and that's the part I think is a bit odd. Whether I feel odd or not is irrelevant tho - it's already there. > > Any better ideas? > > Well. As a simple (probably temporary) fix, I'd suggest > > #define wait_event_freezekillable(wq, condition) > { > freezer_do_not_count(); > __retval = wait_event_killable(condition); > freezer_count(); > __retval; > } > > Do you think it can work? Yeah, probably. I was hoping to remove count/do_not_count tho. Hmmm... maybe we can just flip PF_NOFREEZE instead with a bit of modification, I think. Thanks. -- tejun