diff options
author | Peter Xu <peterx@redhat.com> | 2021-07-22 13:58:37 -0400 |
---|---|---|
committer | Dr. David Alan Gilbert <dgilbert@redhat.com> | 2021-07-26 12:44:26 +0100 |
commit | 53021ea1659b8a9074c6f5eb6c65a4e5dddddaec (patch) | |
tree | 51dbcc6e1005135dc8b6a69c7c4c5aa9dfd80e7a /migration/migration.h | |
parent | 5e32ffd346429b2e92545c425de96d92e88a7498 (diff) |
migration: Fix missing join() of rp_thread
It's possible that the migration thread skip the join() of the rp_thread in
below race and crash on src right at finishing migration:
migration_thread rp_thread
---------------- ---------
migration_completion()
(before rp_thread quits)
from_dst_file=NULL
[thread got scheduled out]
s->rp_state.from_dst_file==NULL
(skip join() of rp_thread)
migrate_fd_cleanup()
qemu_fclose(s->to_dst_file)
yank_unregister_instance()
assert(yank_find_entry()) <------- crash
It could mostly happen with postcopy, but that shouldn't be required, e.g., I
think it could also trigger with MIGRATION_CAPABILITY_RETURN_PATH set.
It's suspected that above race could be the root cause of a recent (but rare)
migration-test break reported by either Dave or PMM:
https://lore.kernel.org/qemu-devel/YPamXAHwan%2FPPXLf@work-vm/
The issue is: from_dst_file is reset in the rp_thread, so if the thread reset
it to NULL fast enough then the migration thread will assume there's no
rp_thread at all.
This could potentially cause more severe issue (e.g. crash) after the yank code.
Fix it by using a boolean to keep "whether we've created rp_thread".
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210722175841.938739-2-peterx@redhat.com>
Reviewed-by: Lukas Straub <lukasstraub2@web.de>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Diffstat (limited to 'migration/migration.h')
-rw-r--r-- | migration/migration.h | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/migration/migration.h b/migration/migration.h index 2ebb740dfa..c302879fad 100644 --- a/migration/migration.h +++ b/migration/migration.h @@ -195,6 +195,13 @@ struct MigrationState { QEMUFile *from_dst_file; QemuThread rp_thread; bool error; + /* + * We can also check non-zero of rp_thread, but there's no "official" + * way to do this, so this bool makes it slightly more elegant. + * Checking from_dst_file for this is racy because from_dst_file will + * be cleared in the rp_thread! + */ + bool rp_thread_created; QemuSemaphore rp_sem; } rp_state; |