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bh=ecw+/l7luLc7WvskempfGO0Am9K8TfzYcmpD33bw7Uo=; b=KUpweo0kTAbXLcqTx+1lN+pX63D6EvZMHLdfZ3CzoDYhl3HbTfYhlFwl/KIKHwMyFirDc6 9F5hGDVa/vUvtjnUr3UlqRBPiO2cwPd+MLuDY2wbzRMfqAQN+hhLquKXKk/ZlrUnZAQTBO pCA1MAoolnWMDvQM1zPx4CojIDwB31U= X-MC-Unique: Mu7haeCWPqCcNjGGoTa9CA-1 From: "Dr. David Alan Gilbert (git)" To: qemu-devel@nongnu.org, yubihong@huawei.com, peterx@redhat.com, peter.maydell@linaro.org Subject: [PULL 15/16] migration/postcopy: Release fd before going into 'postcopy-pause' Date: Mon, 26 Oct 2020 16:19:51 +0000 Message-Id: <20201026161952.149188-16-dgilbert@redhat.com> In-Reply-To: <20201026161952.149188-1-dgilbert@redhat.com> References: <20201026161952.149188-1-dgilbert@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; 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charset="utf-8" From: Peter Xu 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 Reviewed-by: Dr. David Alan Gilbert Signed-off-by: Peter Xu Message-Id: <20201021212721.440373-6-peterx@redhat.com> Signed-off-by: Dr. David Alan Gilbert --- migration/migration.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/migration/migration.c b/migration/migration.c index 5421042d4a..627f194b8b 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -3178,9 +3178,6 @@ static MigThrError postcopy_pause(MigrationState *s) while (true) { QEMUFile *file; =20 - 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); @@ -3191,6 +3188,9 @@ static MigThrError postcopy_pause(MigrationState *s) qemu_file_shutdown(file); qemu_fclose(file); =20 + migrate_set_state(&s->state, s->state, + MIGRATION_STATUS_POSTCOPY_PAUSED); + error_report("Detected IO failure for postcopy. " "Migration paused."); =20 --=20 2.28.0