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[2003:cf:d740:65be:3d79:757f:8d1:97f5]) by smtp.gmail.com with ESMTPSA id bp9-20020a5d5a89000000b0033b4796641asm6199373wrb.22.2024.02.12.00.52.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 12 Feb 2024 00:52:45 -0800 (PST) Message-ID: <76457a47-f011-426c-94ac-a3c4c163c821@redhat.com> Date: Mon, 12 Feb 2024 09:52:44 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/2] block: Allow concurrent BB context changes To: Michael Tokarev , qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, qemu-stable@nongnu.org, Stefan Hajnoczi , Kevin Wolf , Paolo Bonzini , Fam Zheng References: <20240202144755.671354-1-hreitz@redhat.com> <9bc07eef-da55-4ebf-a4ee-1d55eb6fd921@tls.msk.ru> <272941d6-fb76-4c5c-968e-d441c7957646@redhat.com> <62012f98-f2a5-4a28-aec6-3f03b1c5feab@tls.msk.ru> Content-Language: en-US From: Hanna Czenczek In-Reply-To: <62012f98-f2a5-4a28-aec6-3f03b1c5feab@tls.msk.ru> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=hreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.677, 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_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 10.02.24 09:46, Michael Tokarev wrote: > 09.02.2024 19:51, Hanna Czenczek : >> On 09.02.24 15:08, Michael Tokarev wrote: >>> 02.02.2024 17:47, Hanna Czenczek : >>>> Hi, >>>> >>>> Without the AioContext lock, a BB's context may kind of change at any >>>> time (unless it has a root node, and I/O requests are pending). That >>>> also means that its own context (BlockBackend.ctx) and that of its >>>> root >>>> node can differ sometimes (while the context is being changed). >>> >>> How relevant this is for -stable (8.2 at least) which does not have >>> "scsi: eliminate AioContext lock" patchset, and in particular,: >>> v8.2.0-124-geaad0fe260 "scsi: only access SCSIDevice->requests from >>> one thread"? >>> >>> The issue first patch "block-backend: Allow concurrent context changes" >>> fixes (RHEL-19381) seems to be for 8.1.something, so it exists in 8.2 >>> too, and this particular fix applies to 8.2. >>> >>> But with other changes around all this, I'm a bit lost as of what >>> should >>> be done on stable.  Not even thinking about 7.2 here :) >> >> Ah, sorry, yes.  Since we do still have the AioContext lock, this >> series won’t be necessary in -stable.  Sorry for the noise! > > Hm. Now I'm confused even more.. :) > > ad89367202 "block-backend: Allow concurrent context changes" - the first > one in this series - apparently is needed, as it fixes an issue reported > for qemu 8.1 (https://issues.redhat.com/browse/RHEL-19381).  Or is it not > the case? Ah, yes, I got confused there.  There are two (unfortunately? fortunately? Red-Hat-internal) comments, one of which describes the crash that’s fixed here, so I thought that bug described this crash.  But the actual description in the report describes something different (more like what’s fixed by https://lists.nongnu.org/archive/html/qemu-devel/2024-01/msg03649.html, but I’m not entirely sure yet). So basically I got the bug link wrong.  We now have https://issues.redhat.com/browse/RHEL-24593, which has been reported only against 8.2. Hanna > FWIW, truth is born in the noise, not in silence ;) > > Thanks, > > /mjt >