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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 71DA9C77B75 for ; Wed, 17 May 2023 17:10:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229521AbjEQRK1 (ORCPT ); Wed, 17 May 2023 13:10:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55040 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229449AbjEQRKY (ORCPT ); Wed, 17 May 2023 13:10:24 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9748E198E for ; Wed, 17 May 2023 10:09:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1684343378; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=O77FUeBqVv09R6tDA90nsHnvloA7B+EnHXU7+4rYNQ0=; b=fPvpzaO2Gk6R4KtWGq9DCQNxCSK+V7Rz2DIt96VfJivyaN77ps4Z7pQrfiu8emViFPvvzK ng34wrILNepk+/dbOE45zyGaYvgzdc9GhAPOa/XcxkGiFlrcjpufQyzTChxEFWYIerRcqs zhLwhk2gI+gfJvtxj3KGteUHwPDiaNk= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-221-3nq0b3zjNVGGhTxPrHkZdA-1; Wed, 17 May 2023 13:09:37 -0400 X-MC-Unique: 3nq0b3zjNVGGhTxPrHkZdA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id BC7AB185A7A4; Wed, 17 May 2023 17:09:36 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.225.8]) by smtp.corp.redhat.com (Postfix) with SMTP id 22B9EC15BA0; Wed, 17 May 2023 17:09:32 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 17 May 2023 19:09:22 +0200 (CEST) Date: Wed, 17 May 2023 19:09:18 +0200 From: Oleg Nesterov To: "Eric W. Biederman" Cc: Linus Torvalds , Mike Christie , Christian Brauner , Thorsten Leemhuis , nicolas.dichtel@6wind.com, Linux kernel regressions list , hch@infradead.org, stefanha@redhat.com, jasowang@redhat.com, mst@redhat.com, sgarzare@redhat.com, virtualization@lists.linux-foundation.org, konrad.wilk@oracle.com, linux-kernel@vger.kernel.org, Jens Axboe Subject: Re: [PATCH v11 8/8] vhost: use vhost_tasks for worker threads Message-ID: <20230517170917.GA17016@redhat.com> References: <78c5e150-26cf-7724-74ee-4a0b16b944b1@oracle.com> <48842e92-835e-bc3f-7118-48b8f415f532@leemhuis.info> <20230515-vollrausch-liebgeworden-2765f3ca3540@brauner> <122b597e-a5fa-daf7-27bb-6f04fa98d496@oracle.com> <87cz30s20y.fsf@email.froward.int.ebiederm.org> <20230516183757.GA1286@redhat.com> <87mt24ox2d.fsf@email.froward.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87mt24ox2d.fsf@email.froward.int.ebiederm.org> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/16, Eric W. Biederman wrote: > > Oleg Nesterov writes: > > >> There is this bit in complete_signal when SIGKILL is delivered to any > >> thread in the process. > >> > >> t = p; > >> do { > >> task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK); > >> sigaddset(&t->pending.signal, SIGKILL); > >> signal_wake_up(t, 1); > >> } while_each_thread(p, t); > > > > That is why the latest version adds try_set_pending_sigkill(). No, no, > > it is not that I think this is a good idea. > > I see that try_set_pending_sigkill in the patch now. > > That try_set_pending_sigkill just keeps the process from reporting > that it has exited, and extend the process exit indefinitely. > > SIGNAL_GROUP_EXIT has already been set, so the KILL signal was > already delivered and the process is exiting. Agreed, that is why I said I don't think try_set_pending_sigkill() is a good idea. And again, the same is true for the threads created by create_io_thread(). get_signal() from io_uring/ can dequeue a pending SIGKILL and return, but that is all. > >> For clarity that sigaddset(&t->pending.signal, SIGKILL); Really isn't > >> setting SIGKILL pending, > > > > Hmm. it does? Nevermind. > > The point is that what try_set_pending_sigkill in the patch is doing is > keeping the "you are dead exit now" flag, from being set. > > That flag is what fatal_signal_pending always tests, because we can only > know if a fatal signal is pending if we have performed short circuit > delivery on the signal. > > The result is the effects of the change are mostly what people expect. > The difference the semantics being changed aren't what people think they > are. > > AKA process exit is being ignored for the thread, not that SIGKILL is > being blocked. Sorry, I don't understand. I just tried to say that sigaddset(&t->pending.signal, SIGKILL) really sets SIGKILL pending. Nevermind. > > Although I never understood this logic. I meant I never really liked how io-threads play with signals, > I can't even understand the usage > > of lower_32_bits() in create_io_thread(). > > As far as I can tell lower_32_bits(flags) is just defensive programming Cough. but this is ugly. Or I missed something. > or have just populated .flags directly. Exactly, > Then .exit_signal > could have been set to 0. Exactly. ------------------------------------------------------------------------------- OK. It doesn't matter. I tried to read the whole thread and got lost. IIUC, Mike is going to send the next version? So I think we can delay the further discussions until then. Oleg.