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Tue, 25 Jun 2019 17:29:33 +0000 (GMT) From: Nathan Lynch To: Juliet Kim Subject: Re: [PATCH] powerpc/rtas: Fix hang in race against concurrent cpu offline In-Reply-To: <5d116143.403IF78HZadonD0m%julietk@linux.vnet.ibm.com> References: <5d116143.403IF78HZadonD0m%julietk@linux.vnet.ibm.com> Date: Tue, 25 Jun 2019 12:29:32 -0500 Message-ID: <87a7e5tvyb.fsf@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-06-25_12:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=876 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906250131 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: linuxppc-dev@lists.ozlabs.org, mmc@linux.vnet.ibm.com, mwb@linux.ibm.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Juliet Kim writes: > The commit > (=E2=80=9Cpowerpc/rtas: Fix a potential race between CPU-Offline & Migrat= ion) > attempted to fix a hang in Live Partition Mobility(LPM) by abandoning > the LPM attempt if a race between LPM and concurrent CPU offline was > detected. > > However, that fix failed to notify Hypervisor that the LPM attempted > had been abandoned which results in a system hang. It is surprising to me that leaving a migration unterminated would cause Linux to hang. Can you explain more about how that happens? > Fix this by sending a signal PHYP to cancel the migration, so that PHYP > can stop waiting, and clean up the migration. This is well-spotted and rtas_ibm_suspend_me() needs to signal cancellation in several error paths. But I don't agree that this is one of them: this race is going to be a temporary condition in any production setting, and retrying would allow the migration to succeed.