On Wed, Jul 21, 2021 at 03:34:06PM -0400, Peter Xu wrote: > Accessing from_dst_file is potentially racy in current code base like below: > > if (s->from_dst_file) > do_something(s->from_dst_file); > > Because from_dst_file can be reset right after the check in another > thread (rp_thread). One example is migrate_fd_cancel(). > > Use the same qemu_file_lock to protect it too, just like to_dst_file. > > When it's safe to access without lock, comment it. > > There's one special reference in migration_thread() that can be replaced by > the newly introduced rp_thread_created flag. > > Reported-by: Dr. David Alan Gilbert <dgilb...@redhat.com> > Signed-off-by: Peter Xu <pet...@redhat.com> > --- > migration/migration.c | 32 +++++++++++++++++++++++++------- > migration/migration.h | 8 +++++--- > migration/ram.c | 1 + > 3 files changed, 31 insertions(+), 10 deletions(-) > > diff --git a/migration/migration.c b/migration/migration.c > index 21b94f75a3..fa70400f98 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -1879,10 +1879,12 @@ static void migrate_fd_cancel(MigrationState *s) > QEMUFile *f = migrate_get_current()->to_dst_file; > trace_migrate_fd_cancel(); > > + qemu_mutex_lock(&s->qemu_file_lock); > if (s->rp_state.from_dst_file) { > /* shutdown the rp socket, so causing the rp thread to shutdown */ > qemu_file_shutdown(s->rp_state.from_dst_file); > } > + qemu_mutex_unlock(&s->qemu_file_lock);
Worth using WITH_QEMU_LOCK_GUARD? > @@ -2827,11 +2845,13 @@ out: > * Maybe there is something we can do: it looks like a > * network down issue, and we pause for a recovery. > */ > - qemu_fclose(rp); > - ms->rp_state.from_dst_file = NULL; > + migration_release_from_dst_file(ms); > rp = NULL; > if (postcopy_pause_return_path_thread(ms)) { > - /* Reload rp, reset the rest */ > + /* > + * Reload rp, reset the rest. Referencing it is save since s/save/safe/ > + * it's reset only by us above, or when migration completes > + */ > rp = ms->rp_state.from_dst_file; > ms->rp_state.error = false; > goto retry; -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org