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Lunev" Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, Hanna Reitz , Vladimir Sementsov-Ogievskiy , Andrey Drobyshev Subject: Re: [PATCH v2 0/3] block/accounting: fix unlocked latency histogram reconfiguration races Message-ID: References: <20260724111311.4086859-1-den@openvz.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260724111311.4086859-1-den@openvz.org> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.419, 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_PASS=-0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development 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 Am 24.07.2026 um 13:13 hat Denis V. Lunev geschrieben: > block_latency_histogram_set() and block_latency_histograms_clear() > replace BlockLatencyHistogram's nbins/boundaries/bins without taking > stats->lock, while block_account_one_io() reads those same fields > under that lock from whatever iothread completes the I/O. A histogram > reconfiguration (block-latency-histogram-set QMP command, monitor > thread) racing an in-flight completion can therefore observe those > fields torn, hitting assert(pos != NULL) in > block_latency_histogram_account(), or corrupting the heap outright. > This showed up as a qemu-kvm SIGABRT on a customer's virtio-blk guest. > > Regression test is added for illustrative purpose but I am unsure that > it is viable long term. Feel free to drop. > > v1 -> v2 > * patch 1, 2: WITH_QEMU_LOCK_GUARD -> plain lock()/unlock(), pure > additions, nothing reindented or moved > * patch 3: writer thread now also calls > block_latency_histograms_clear(), the other function patch 1 fixes > * patch 2: take stats->lock for bdrv_query_blk_stats()'s whole call > instead of per-section, since the interval loop's > timed_average_min/max/avg() calls race timed_average_account() the > same way the already-locked fields did; block_acct_queue_depth() > now requires the caller to hold the lock instead of taking it > itself, since bdrv_query_blk_stats() is its only caller Thanks, applied to the block branch. Kevin