From d246ea5039fd6d5344becd0943fcbb7f8e6bbfe7 Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Wed, 21 Oct 2020 17:27:20 -0400 Subject: [PATCH] migration/postcopy: Release fd before going into 'postcopy-pause' 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; - 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); + migrate_set_state(&s->state, s->state, + MIGRATION_STATUS_POSTCOPY_PAUSED); + error_report("Detected IO failure for postcopy. " "Migration paused.");