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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A2DB7C3DA64 for ; Wed, 31 Jul 2024 15:22:19 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sZB91-0002ix-B6; Wed, 31 Jul 2024 11:21:39 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sZB8z-0002i8-Fp for qemu-devel@nongnu.org; Wed, 31 Jul 2024 11:21:37 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sZB8x-0006hy-PK for qemu-devel@nongnu.org; Wed, 31 Jul 2024 11:21:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1722439294; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=pTogfFo0xxLk8tiw+WEKKwv4Dvgm3icbEeGCSVYs5+c=; b=ZQYZu9JfDMkeD+UMjIUPp0gaDpuMSPrPK0FRBE19rASDjHAQYgonEh0FFI679idclkTosT 10roEe44V0seZ7ehArfQu5jcblwjROj0qdJZLH0UB/Rwi+8T+ky1wnvCCJ0CoJ6m+cZy6a SwEkWNi/Rb8pOmx0Z2r42PvCzXn0UDA= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-633-0Cl10TstOTCdyLIDF3mQfQ-1; Wed, 31 Jul 2024 11:21:30 -0400 X-MC-Unique: 0Cl10TstOTCdyLIDF3mQfQ-1 Received: from mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.15]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 097931977025; Wed, 31 Jul 2024 15:21:13 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.33]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 6736F1955D42; Wed, 31 Jul 2024 15:21:09 +0000 (UTC) Date: Wed, 31 Jul 2024 16:21:05 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Peter Maydell Cc: Philipp Reisner , qemu-devel@nongnu.org, Fabiano Rosas , Peter Xu , Paolo Bonzini , David Hildenbrand Subject: Re: [PATCH] util: retry open() when it gets interrupted by a signal Message-ID: References: <20240731132524.308273-1-philipp.reisner@linbit.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.12 (2023-09-09) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.126, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Jul 31, 2024 at 03:32:52PM +0100, Peter Maydell wrote: > On Wed, 31 Jul 2024 at 15:11, Daniel P. Berrangé wrote: > > > > On Wed, Jul 31, 2024 at 03:25:24PM +0200, Philipp Reisner wrote: > > > As with many syscalls, open() might be interrupted by a signal. > > > > > > The experienced logfile entry is: > > > > > > qemu-system-x86_64: -device virtio-blk-pci,bus=pci.0,addr=0x7,drive=libvirt-2-format,id=virtio-disk0,bootindex=2,write-cache=on,serial=1b990c4d13b74a4e90ea: Could not open '/dev/drbd1003': Interrupted system call What is the actual signal you are seeing that impacts QEMU in this way ? > > > Retry it until it is not interrupted by a signal. > > > > As you say, many syscalls can be interruptted by signals, so > > special casing open() isn't really a solution - its just > > addressing one specific instance you happened to see. > > > > If there are certain signals that we don't want to have a > > fatal interruption for, it'd be better to set SA_RESTART > > with sigaction, which will auto-restart a large set of > > syscalls, while allowing other signals to be fatal. > > This is why we have the RETRY_ON_EINTR() macro, right? > > Currently we have some places that call qemu_open_old() inside > RETRY_ON_EINTR -- we should decide whether we want to > handle EINTR inside the qemu_open family of functions, > or make the caller deal with it, and put the macro uses > in the right place consistently. It is incredibly arbitrary where we use RETRY_ON_EINTR, which I think points towards it being a sub-optimal solution to the general problem. > > I agree that it would be nicer if we could use SA_RESTART, > but presumably there's a reason why we don't. (At any > rate code that's shared with the user-mode emulation > has to be EINTR-resistant, because we can't force the > user-mode guest code to avoid registering signal handlers > that aren't SA_RESTART.) For user mode emulation isn't it valid to just propagage the EINTR back up to the application, since EINTR is a valid errno they have to be willing to handle unless the app has itself use SA_RESTART. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|