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[58.6.239.121]) by smtp.gmail.com with ESMTPSA id r2sm14047813pgv.50.2021.03.15.19.37.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Mar 2021 19:37:20 -0700 (PDT) Date: Tue, 16 Mar 2021 12:37:15 +1000 From: Nicholas Piggin Subject: Re: [PATCH 0/2] handle premature return from H_JOIN in pseries mobility code To: linuxppc-dev@lists.ozlabs.org, Nathan Lynch References: <20210315080045.460331-1-nathanl@linux.ibm.com> In-Reply-To: <20210315080045.460331-1-nathanl@linux.ibm.com> MIME-Version: 1.0 Message-Id: <1615861985.myhwki4p5y.astroid@bobo.none> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: brking@linux.ibm.com, tyreld@linux.ibm.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Excerpts from Nathan Lynch's message of March 15, 2021 6:00 pm: > pseries VMs in shared processor mode are susceptible to failed > migrations becasue stray H_PRODs from the paravirt spinlock > implementation can bump threads out of joining state before the > suspend has occurred. Fix this by adding a small amount of shared > state and ordering accesses to it with respect to H_PROD and H_JOIN. Oh, tricky problem. Nice work on finding and fixing it. The patches seem okay to me. Thanks, Nick