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Wed, 13 May 2020 12:25:56 +0000 (UTC) Date: Wed, 13 May 2020 13:25:54 +0100 From: "Dr. David Alan Gilbert" To: Paolo Bonzini Subject: Re: [PATCH 0/5] Introduce 'yank' oob qmp command to recover from hanging qemu Message-ID: <20200513122554.GH3225@work-vm> References: <20200511120718.GD2811@work-vm> <20200511121714.GL1135885@redhat.com> <20200511154645.GI2811@work-vm> <20200512113206.62836e44@luklap> <20200512094337.GK1191162@redhat.com> <20200513103245.GD6202@linux.fritz.box> <20200513105359.GF3225@work-vm> <20200513111320.GE6202@linux.fritz.box> <20200513112630.GJ1215285@redhat.com> <31bb69c3-5149-70cf-7527-54680b1e3f6b@redhat.com> MIME-Version: 1.0 In-Reply-To: <31bb69c3-5149-70cf-7527-54680b1e3f6b@redhat.com> User-Agent: Mutt/1.13.4 (2020-02-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.81; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/13 04:17:42 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, 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_H2=-0.001, SPF_PASS=-0.001, T_HK_NAME_DR=0.01 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Lukas Straub , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , qemu-block , Juan Quintela , qemu-devel , Max Reitz , =?iso-8859-1?Q?Marc-Andr=E9?= Lureau Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Paolo Bonzini (pbonzini@redhat.com) wrote: > On 13/05/20 13:26, Daniel P. Berrangé wrote: > > Are you referring to the in-kernel NFS client hangs here ? AFAIK, it is > > impossible to do anything to get out of those hangs from userspace, because > > the thread is stuck in an uninterruptable sleep in kernel space. > > > > If using the in-QEMU NFS client, then there is a network connection that > > can be yanked just like the NBD client. > > But it's a bad idea to yank it (and also the NBD client) because you're > not sure which wites have made it to the server (and to the medium) and > which haven't. No, that's OK - if you look at the COLO case, and some other cases, you've got a dead storage device but your redundant pair might be OK; so it's OK to yank it. Other similar storage cases are trying to migrate a VM that has one dead disk, even if you know and accept it's dead and unresponding, you often can't kill it off if the device is hung. > Effectively, the in-QEMU NFS client and NBD client are always operating > in "soft" mode, but we should always treat that as a bug (which cannot > be fixed) and not a feature for read-write images. Dave > > Paolo > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK