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[184.147.14.204]) by smtp.gmail.com with ESMTPSA id o4sm2040873qkk.75.2020.10.07.11.33.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Oct 2020 11:33:26 -0700 (PDT) From: Peter Xu To: qemu-devel@nongnu.org Subject: [PATCH] migration/postcopy: Release fd before going into 'postcopy-pause' Date: Wed, 7 Oct 2020 14:33:24 -0400 Message-Id: <20201007183324.288379-1-peterx@redhat.com> X-Mailer: git-send-email 2.26.2 MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Received-SPF: pass client-ip=216.205.24.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/07 00:54:30 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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=-0.742, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, 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: , Cc: "Dr . David Alan Gilbert" , peterx@redhat.com, Juan Quintela Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Logically below race could trigger with the old code: test program migration thread ------------ ---------------- wait_until('postcopy-pause') postcopy_pause() set_state('postcopy-pause') do_postcopy_recover() arm s->to_dst_file with new fd release s->to_dst_file [1] Here [1] could have released the just-installed recoverying channel. Then the migration could hang without really resuming. Instead, it should be very safe to release the fd before setting the state into 'postcopy-pause', because there's no reason for any other thread to touch it during 'postcopy-active'. Dave reported a very rare postcopy recovery hang that the migration-test program waited for the migration to complete in migrate_postcopy_complete(). We do suspect it's the same thing that we're gonna fix here. Hard to tell. However since we've noticed this, fix this irrelevant of the hang report. Cc: Dr. David Alan Gilbert Cc: Juan Quintela Signed-off-by: Peter Xu --- migration/migration.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/migration/migration.c b/migration/migration.c index aca7fdcd0b..e1b06e8a2a 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -3137,9 +3137,6 @@ static MigThrError postcopy_pause(MigrationState *s) while (true) { QEMUFile *file; - migrate_set_state(&s->state, s->state, - MIGRATION_STATUS_POSTCOPY_PAUSED); - /* Current channel is possibly broken. Release it. */ assert(s->to_dst_file); qemu_mutex_lock(&s->qemu_file_lock); @@ -3150,6 +3147,9 @@ static MigThrError postcopy_pause(MigrationState *s) qemu_file_shutdown(file); qemu_fclose(file); + migrate_set_state(&s->state, s->state, + MIGRATION_STATUS_POSTCOPY_PAUSED); + error_report("Detected IO failure for postcopy. " "Migration paused.");