* [PATCH] migration/postcopy: Release fd before going into 'postcopy-pause'
@ 2020-10-07 18:33 Peter Xu
0 siblings, 0 replies; only message in thread
From: Peter Xu @ 2020-10-07 18:33 UTC (permalink / raw)
To: qemu-devel; +Cc: Dr . David Alan Gilbert, peterx, Juan Quintela
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 <dgilbert@redhat.com>
Cc: Juan Quintela <quintela@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
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.");
--
2.26.2
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2020-10-07 18:33 [PATCH] migration/postcopy: Release fd before going into 'postcopy-pause' Peter Xu
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