From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43375) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1e4kCT-0002u2-Gl for qemu-devel@nongnu.org; Wed, 18 Oct 2017 04:59:42 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1e4kCN-0007Vz-OW for qemu-devel@nongnu.org; Wed, 18 Oct 2017 04:59:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44540) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1e4kCN-0007Uk-FS for qemu-devel@nongnu.org; Wed, 18 Oct 2017 04:59:35 -0400 Date: Wed, 18 Oct 2017 09:59:27 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20171018085927.GA2339@work-vm> References: <20171011191317.24157-1-dgilbert@redhat.com> <20171011191317.24157-4-dgilbert@redhat.com> <20171018033519.GM4166@pxdev.xzpeter.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171018033519.GM4166@pxdev.xzpeter.org> Subject: Re: [Qemu-devel] [PATCH 3/7] migration: Wait for semaphore before completing migration List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Xu Cc: qemu-devel@nongnu.org, kwolf@redhat.com, jdenemar@redhat.com, wangjie88@huawei.com, quintela@redhat.com, mreitz@redhat.com, berrange@redhat.com, eblake@redhat.com, fuweiwei2@huawei.com * Peter Xu (peterx@redhat.com) wrote: > On Wed, Oct 11, 2017 at 08:13:13PM +0100, Dr. David Alan Gilbert (git) wrote: > > From: "Dr. David Alan Gilbert" > > > > Wait for a semaphore before completing the migration, > > if the previously added capability was enabled. > > > > Signed-off-by: Dr. David Alan Gilbert > > --- > > migration/migration.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++ > > migration/migration.h | 3 +++ > > 2 files changed, 50 insertions(+) > > > > diff --git a/migration/migration.c b/migration/migration.c > > index e1a87c3d23..b411a7bb63 100644 > > --- a/migration/migration.c > > +++ b/migration/migration.c > > @@ -1967,6 +1967,46 @@ fail: > > } > > > > /** > > + * migration_maybe_pause: Pause if required to by migrate_pause_before_device > > + * called with the iothread locked > > + * Returns: 0 on success > > + */ > > +static int migration_maybe_pause(MigrationState *s, int *current_active_state) > > +{ > > + int ret; > > + if (!migrate_pause_before_device()) { > > + return 0; > > + } > > + ret = bdrv_inactivate_all(); > > My understanding is that the crash was caused by mirrored block device > IO triggered after the inactivation, then... should we do this after > waiting for the semaphore (possibly at [1] below) to make sure the > block jobs are completed? Or did I miss anything? Ah you're right, just confirmed this with kwolf that I got it the wrong way around. I'll fix it. Dave > > + if (ret) { > > + error_report("%s: bdrv_inactivate_all() failed (%d)", > > + __func__, ret); > > + return ret; > > + } > > + > > + s->block_inactive = true; > > + > > + /* Since leaving this state is not atomic with posting the semaphore > > + * it's possible that someone could have issued multiple migrate_continue > > + * and the semaphore is incorrectly positive at this point; > > + * the docs say it's undefined to reinit a semaphore that's already > > + * init'd, so use timedwait to eat up any existing posts. > > + */ > > + while (qemu_sem_timedwait(&s->pause_sem, 1) == 0); > > + > > + qemu_mutex_unlock_iothread(); > > + migrate_set_state(&s->state, *current_active_state, > > + MIGRATION_STATUS_PAUSE_BEFORE_DEVICE); > > + qemu_sem_wait(&s->pause_sem); > > [1] > > > + migrate_set_state(&s->state, MIGRATION_STATUS_PAUSE_BEFORE_DEVICE, > > + MIGRATION_STATUS_DEVICE); > > + *current_active_state = MIGRATION_STATUS_DEVICE; > > + qemu_mutex_lock_iothread(); > > + > > + return s->state == MIGRATION_STATUS_DEVICE ? 0 : -EINVAL; > > +} > > + > > +/** > > * migration_completion: Used by migration_thread when there's not much left. > > * The caller 'breaks' the loop when this returns. > > * > > @@ -1992,6 +2032,11 @@ static void migration_completion(MigrationState *s, int current_active_state, > > bool inactivate = !migrate_colo_enabled(); > > ret = vm_stop_force_state(RUN_STATE_FINISH_MIGRATE); > > if (ret >= 0) { > > + ret = migration_maybe_pause(s, ¤t_active_state); > > + /* If this worked it will already have inactivated */ > > + inactivate &= !migrate_pause_before_device(); > > + } > > + if (ret >= 0) { > > qemu_file_set_rate_limit(s->to_dst_file, INT64_MAX); > > ret = qemu_savevm_state_complete_precopy(s->to_dst_file, false, > > inactivate); > > @@ -2372,6 +2417,7 @@ static void migration_instance_finalize(Object *obj) > > > > g_free(params->tls_hostname); > > g_free(params->tls_creds); > > + qemu_sem_destroy(&ms->pause_sem); > > } > > > > static void migration_instance_init(Object *obj) > > @@ -2382,6 +2428,7 @@ static void migration_instance_init(Object *obj) > > ms->state = MIGRATION_STATUS_NONE; > > ms->xbzrle_cache_size = DEFAULT_MIGRATE_CACHE_SIZE; > > ms->mbps = -1; > > + qemu_sem_init(&ms->pause_sem, 0); > > > > params->tls_hostname = g_strdup(""); > > params->tls_creds = g_strdup(""); > > diff --git a/migration/migration.h b/migration/migration.h > > index 37feea5453..447e8b3f79 100644 > > --- a/migration/migration.h > > +++ b/migration/migration.h > > @@ -121,6 +121,9 @@ struct MigrationState > > /* Flag set once the migration thread called bdrv_inactivate_all */ > > bool block_inactive; > > > > + /* Migration is paused due to pause-before-device */ > > + QemuSemaphore pause_sem; > > + > > /* The semaphore is used to notify COLO thread that failover is finished */ > > QemuSemaphore colo_exit_sem; > > > > -- > > 2.13.6 > > > > -- > Peter Xu -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK