From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1B2FCC28CC0 for ; Thu, 30 May 2019 01:54:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D8B0E24400 for ; Thu, 30 May 2019 01:54:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727346AbfE3ByU (ORCPT ); Wed, 29 May 2019 21:54:20 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:54155 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726527AbfE3ByU (ORCPT ); Wed, 29 May 2019 21:54:20 -0400 Received: from in01.mta.xmission.com ([166.70.13.51]) by out01.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.87) (envelope-from ) id 1hWAGm-0003tx-S1; Wed, 29 May 2019 19:54:16 -0600 Received: from ip72-206-97-68.om.om.cox.net ([72.206.97.68] helo=x220.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.87) (envelope-from ) id 1hWAGl-0003zx-2c; Wed, 29 May 2019 19:54:16 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Arnd Bergmann Cc: Oleg Nesterov , Deepa Dinamani , Al Viro , Linus Torvalds , Linux Kernel Mailing List , Andrew Morton , dbueso@suse.de, Jens Axboe , Davidlohr Bueso , e@80x24.org, Jason Baron , Linux FS-devel Mailing List , linux-aio , omar.kilani@gmail.com, Thomas Gleixner , "# 3.4.x" References: <20190522032144.10995-1-deepa.kernel@gmail.com> <20190529161157.GA27659@redhat.com> Date: Wed, 29 May 2019 20:54:09 -0500 In-Reply-To: (Arnd Bergmann's message of "Thu, 30 May 2019 00:32:32 +0200") Message-ID: <874l5czozi.fsf@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1hWAGl-0003zx-2c;;;mid=<874l5czozi.fsf@xmission.com>;;;hst=in01.mta.xmission.com;;;ip=72.206.97.68;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+sYXiM8eraUyZMQcF4BEIK0Zqv4Ek0euE= X-SA-Exim-Connect-IP: 72.206.97.68 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: pselect/etc semantics X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org Arnd Bergmann writes: > On Wed, May 29, 2019 at 6:12 PM Oleg Nesterov wrote: >> >> Al, Linus, Eric, please help. >> >> The previous discussion was very confusing, we simply can not understand each >> other. >> >> To me everything looks very simple and clear, but perhaps I missed something >> obvious? Please correct me. > > Thanks for the elaborate explanation in this patch, it all starts making sense > to me now. I also looked at your patch in detail and thought I had found > a few mistakes at first but those all turned out to be mistakes in my reading. > >> See the compile-tested patch at the end. Of course, the new _xxx() helpers >> should be renamed somehow. fs/aio.c doesn't look right with or without this >> patch, but iiuc this is what it did before 854a6ed56839a. > > I think this is a nice simplification, but it would help not to mix up the > minimal regression fix with the rewrite of those functions. For the stable > kernels, I think we want just the addition of the 'bool interrupted' argument > to restore_user_sigmask() to close the race that was introduced > 854a6ed56839a. Following up on that for future kernels, your patch > improves the readability, but we can probably take it even further. > >> - ret = set_user_sigmask(ksig.sigmask, &ksigmask, &sigsaved, ksig.sigsetsize); >> + ret = set_xxx(ksig.sigmask, ksig.sigsetsize); >> if (ret) >> return ret; >> >> ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &ts : NULL); >> - restore_user_sigmask(ksig.sigmask, &sigsaved); >> - if (signal_pending(current) && !ret) >> + >> + interrupted = signal_pending(current); >> + update_xxx(interrupted); > > Maybe name this > > restore_saved_sigmask_if(!interrupted); > > and make restore_saved_sigmask_if() an inline function > next to restore_saved_sigmask()? > >> @@ -2201,13 +2205,15 @@ COMPAT_SYSCALL_DEFINE6(io_pgetevents, >> if (usig && copy_from_user(&ksig, usig, sizeof(ksig))) >> return -EFAULT; >> >> - ret = set_compat_user_sigmask(ksig.sigmask, &ksigmask, &sigsaved, ksig.sigsetsize); >> + ret = set_compat_xxx(ksig.sigmask, ksig.sigsetsize); >> if (ret) >> return ret; > > With some of the recent discussions about compat syscall handling, > I now think that we want to just fold set_compat_user_sigmask() > into set_user_sigmask() (whatever they get called in the end) > with an in_compat_syscall() conditional inside it, and completely get > rid of the COMPAT_SYSCALL_DEFINEx() definitions for those > system calls for which this is the only difference. > > Unfortunately we still need the time32/time64 distinction, but removing > syscall handlers is a significant cleanup here already, and we can > move most of the function body of sys_io_pgetevents() into > do_io_getevents() in the process. Same for some of the other calls. > > Not sure about the order of the cleanups, but probably something like > this would work: > > 1. fix the race (to be backported) > 2. unify set_compat_user_sigmask/set_user_sigmask > 3. remove unneeded compat handlers > 4. replace restore_user_sigmask with restore_saved_sigmask_if() > 5. also unify compat_get_fd_set()/get_fd_set() and kill off > compat select() variants. Are new system calls added preventing a revert of the patch in question for stable kernels? Eric