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([2001:8b0:aba:5f3c:e4cd:1977:5709:51f0]) by smtp.gmail.com with ESMTPSA id j11sm16589204wms.6.2021.06.29.06.34.47 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Jun 2021 06:34:47 -0700 (PDT) Message-ID: <709a88a0f24ed8fd5399a2be88fb9d57ceb0a25a.camel@linuxfoundation.org> Subject: Re: VMs hanging with rcu stall problems From: Richard Purdie To: qemu-devel Date: Tue, 29 Jun 2021 14:34:46 +0100 In-Reply-To: <89f4220fd2b973ebfed4bf4be0afbdefc44a9d4d.camel@linuxfoundation.org> References: <89f4220fd2b973ebfed4bf4be0afbdefc44a9d4d.camel@linuxfoundation.org> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.40.0-1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::430; envelope-from=richard.purdie@linuxfoundation.org; helo=mail-wr1-x430.google.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.435, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, 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: 2.1.23 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" On Thu, 2021-06-03 at 11:02 +0100, Richard Purdie wrote: > We're seeing intermittent rcu stalls in qemu system mode emulation which is  > causing CI issues for us (Yocto Project). We're struggling to understand > the cause and have tried several things to mitigate without much success.  > The stalls are odd in that the log messages look incomplete. An example > from last night: To answer my own question, the issue is a kernel bug in RCU stall handling. The fix: https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?h=rcu/next&id=c583bcb8f5ed and patch which introduced the problem: https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?h=rcu/next&id=c583bcb8f5ed Cheers, Richard