From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E03FDD10384 for ; Wed, 26 Nov 2025 07:58:20 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vOAPa-0003MZ-4N; Wed, 26 Nov 2025 02:58:02 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vOAPT-0003Jx-R9 for qemu-devel@nongnu.org; Wed, 26 Nov 2025 02:57:55 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vOAPQ-0005Cb-Ua for qemu-devel@nongnu.org; Wed, 26 Nov 2025 02:57:55 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1764143870; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=LrBEnroPxZhQCkkCgPCCspSVlAGSj+0cKqQ2e2b/+J4=; b=E3j0It77ai9OaYMf30jZV2urfbyT1VbxEhJhUmPC3zyoP7oMrMYjN9MuqTRwB8O3ioB6s+ VXRMHagH288XaM4G1i811L0K5Af1BEgfpXOGczpkMA37QjSmAMwckHbuH1XyNoYbgyae9B /mrObKKab7+zuEMFoLxk1mkznhRYitI= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-106-QU0KgaklOF69ONKJRBcwVw-1; Wed, 26 Nov 2025 02:57:47 -0500 X-MC-Unique: QU0KgaklOF69ONKJRBcwVw-1 X-Mimecast-MFC-AGG-ID: QU0KgaklOF69ONKJRBcwVw_1764143866 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5E5DA180047F; Wed, 26 Nov 2025 07:57:46 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.45.242.3]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 904D6195608E; Wed, 26 Nov 2025 07:57:45 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 24A0C21E6A27; Wed, 26 Nov 2025 08:57:43 +0100 (CET) From: Markus Armbruster To: Peter Xu Cc: qemu-devel@nongnu.org, Juraj Marcin , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , Fabiano Rosas , Daniel P . =?utf-8?Q?Berrang=C3=A9?= , Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH for-11.0 6/6] migration: Replace migrate_set_error() with migrate_error_propagate() In-Reply-To: <20251125204648.857018-7-peterx@redhat.com> (Peter Xu's message of "Tue, 25 Nov 2025 15:46:48 -0500") References: <20251125204648.857018-1-peterx@redhat.com> <20251125204648.857018-7-peterx@redhat.com> Date: Wed, 26 Nov 2025 08:57:43 +0100 Message-ID: <87pl95dy4o.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.152, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Peter Xu writes: > migrate_set_error() currently doesn't take ownership of the error being > passed in. It's not aligned with the error API and meanwhile it also > makes most of the caller free the error explicitly. > > Change the API to take the ownership of the Error object instead. When at > it, remove the first parameter so it's friendly to g_clear_pointer(). It > can be used whenever the caller wants to provide extra safety measure (or > reuse the pointer) to reset the Error* pointer after stolen. > > Signed-off-by: Peter Xu Worth mentioning that this avoids Error object copies? > --- > migration/migration.h | 2 +- > migration/cpr-exec.c | 4 +-- > migration/migration.c | 46 +++++++++++++++----------------- > migration/multifd-device-state.c | 5 +--- > migration/multifd.c | 19 +++++++------ > migration/postcopy-ram.c | 5 ++-- > migration/ram.c | 4 +-- > migration/savevm.c | 15 ++++------- > 8 files changed, 42 insertions(+), 58 deletions(-) > > diff --git a/migration/migration.h b/migration/migration.h > index 213b33fe6e..df74f9b14f 100644 > --- a/migration/migration.h > +++ b/migration/migration.h > @@ -525,7 +525,7 @@ void migration_incoming_process(void); > > bool migration_has_all_channels(void); > > -void migrate_set_error(MigrationState *s, const Error *error); > +void migrate_error_propagate(Error *error); > bool migrate_has_error(MigrationState *s); > > void migration_connect(MigrationState *s, Error *error_in); > diff --git a/migration/cpr-exec.c b/migration/cpr-exec.c > index 0b8344a86f..13e6138f56 100644 > --- a/migration/cpr-exec.c > +++ b/migration/cpr-exec.c > @@ -158,9 +158,7 @@ static void cpr_exec_cb(void *opaque) > > error_report_err(error_copy(err)); > migrate_set_state(&s->state, s->state, MIGRATION_STATUS_FAILED); > - migrate_set_error(s, err); > - error_free(err); > - err = NULL; > + g_clear_pointer(&err, migrate_error_propagate); > > /* Note, we can go from state COMPLETED to FAILED */ > migration_call_notifiers(s, MIG_EVENT_PRECOPY_FAILED, NULL); I dislike g_clear_pointer(), and I dislike the change from taking the migration state as argument to getting the global migration state with migrate_get_current(). The loss of similarity to error_propagate() is unfortunate, but tolerable. This is not a demand. For each hunk, we need to prove that the migrate_set_error()'s first argument before the patch equals migrate_get_current() afterwards. For this hunk, it's locally obvious: @s is initialized to migrate_get_current() at the beginning of the funtion. Where it's not locally obvious, I guess we could argue that just one MigrationState object exists, so a MigrationState * can only point to that one. If locally non-obvious hunks exist, such an argument needs to be made in the commit message. I did *not* check this aspect of the patch. > diff --git a/migration/migration.c b/migration/migration.c > index 4fe69cc2ef..219d3129cb 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -914,9 +914,7 @@ process_incoming_migration_co(void *opaque) > fail: > migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE, > MIGRATION_STATUS_FAILED); > - migrate_set_error(s, local_err); > - error_free(local_err); > - > + migrate_error_propagate(local_err); > migration_incoming_state_destroy(); > > if (mis->exit_on_error) { > @@ -1548,14 +1546,22 @@ static void migration_cleanup_bh(void *opaque) > migration_cleanup(opaque); > } > > -void migrate_set_error(MigrationState *s, const Error *error) > +/* > + * Propagate the Error* object to migration core. The caller mustn't > + * reference the error pointer after the function returned, because the > + * Error* object might be freed. > + */ > +void migrate_error_propagate(Error *error) > { > - QEMU_LOCK_GUARD(&s->error_mutex); > + MigrationState *s = migrate_get_current(); > > + QEMU_LOCK_GUARD(&s->error_mutex); > trace_migrate_error(error_get_pretty(error)); > > if (!s->error) { > - s->error = error_copy(error); > + s->error = error; > + } else { > + error_free(error); > } > } > > @@ -1601,8 +1607,7 @@ static void migration_connect_set_error(MigrationState *s, Error *error) > } > > migrate_set_state(&s->state, current, next); > - migrate_set_error(s, error); > - error_free(error); > + migrate_error_propagate(error); > } > > void migration_cancel(void) > @@ -2014,8 +2019,7 @@ void qmp_migrate_pause(Error **errp) > > /* Tell the core migration that we're pausing */ > error_setg(&error, "Postcopy migration is paused by the user"); > - migrate_set_error(ms, error); > - error_free(error); > + migrate_error_propagate(error); > > qemu_mutex_lock(&ms->qemu_file_lock); > if (ms->to_dst_file) { > @@ -2647,8 +2651,7 @@ static void *source_return_path_thread(void *opaque) > > out: > if (err) { > - migrate_set_error(ms, err); > - error_free(err); > + migrate_error_propagate(err); > trace_source_return_path_thread_bad_end(); > } > > @@ -3094,12 +3097,10 @@ static void migration_completion(MigrationState *s) > > fail: > if (qemu_file_get_error_obj(s->to_dst_file, &local_err)) { > - migrate_set_error(s, local_err); > - error_free(local_err); > + migrate_error_propagate(local_err); > } else if (ret) { > error_setg_errno(&local_err, -ret, "Error in migration completion"); > - migrate_set_error(s, local_err); > - error_free(local_err); > + migrate_error_propagate(local_err); > } > > if (s->state != MIGRATION_STATUS_CANCELLING) { > @@ -3326,8 +3327,7 @@ static MigThrError migration_detect_error(MigrationState *s) > } > > if (local_error) { > - migrate_set_error(s, local_error); > - error_free(local_error); > + migrate_error_propagate(local_error); > } > > if (state == MIGRATION_STATUS_POSTCOPY_ACTIVE && ret) { > @@ -3522,7 +3522,7 @@ static MigIterateState migration_iteration_run(MigrationState *s) > if (must_precopy <= s->threshold_size && > can_switchover && qatomic_read(&s->start_postcopy)) { > if (postcopy_start(s, &local_err)) { > - migrate_set_error(s, local_err); > + migrate_error_propagate(error_copy(local_err)); First hunk where we don't save a copy. Reason: we report in addition to propagate. There are a several more below. "Forking" the error like this gives me an uneasy feeling, as explained in Subject: Re: [PATCH 0/3] migration: Error fixes and improvements Date: Tue, 18 Nov 2025 08:44:32 +0100 Message-ID: <87a50jlr8f.fsf@pond.sub.org> Clearly out of scope for this series. > error_report_err(local_err); > } > return MIG_ITERATE_SKIP; > @@ -3819,8 +3819,7 @@ static void *migration_thread(void *opaque) > * devices to unplug. This to preserve migration state transitions. > */ > if (ret) { > - migrate_set_error(s, local_err); > - error_free(local_err); > + migrate_error_propagate(local_err); > migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE, > MIGRATION_STATUS_FAILED); > goto out; > @@ -3944,8 +3943,7 @@ static void *bg_migration_thread(void *opaque) > * devices to unplug. This to preserve migration state transitions. > */ > if (ret) { > - migrate_set_error(s, local_err); > - error_free(local_err); > + migrate_error_propagate(local_err); > migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE, > MIGRATION_STATUS_FAILED); > goto fail_setup; > @@ -4127,7 +4125,7 @@ void migration_connect(MigrationState *s, Error *error_in) > return; > > fail: > - migrate_set_error(s, local_err); > + migrate_error_propagate(error_copy(local_err)); > if (s->state != MIGRATION_STATUS_CANCELLING) { > migrate_set_state(&s->state, s->state, MIGRATION_STATUS_FAILED); > } > diff --git a/migration/multifd-device-state.c b/migration/multifd-device-state.c > index db3239fef5..3040d70872 100644 > --- a/migration/multifd-device-state.c > +++ b/migration/multifd-device-state.c > @@ -143,8 +143,6 @@ static int multifd_device_state_save_thread(void *opaque) > Error *local_err = NULL; > > if (!data->hdlr(data, &local_err)) { > - MigrationState *s = migrate_get_current(); > - > /* > * Can't call abort_device_state_save_threads() here since new > * save threads could still be in process of being launched > @@ -158,8 +156,7 @@ static int multifd_device_state_save_thread(void *opaque) > * In case of multiple save threads failing which thread error > * return we end setting is purely arbitrary. > */ > - migrate_set_error(s, local_err); > - error_free(local_err); > + migrate_error_propagate(local_err); > } > > return 0; > diff --git a/migration/multifd.c b/migration/multifd.c > index c861b4b557..99717b64e9 100644 > --- a/migration/multifd.c > +++ b/migration/multifd.c > @@ -428,8 +428,9 @@ static void multifd_send_set_error(Error *err) > > if (err) { > MigrationState *s = migrate_get_current(); > - migrate_set_error(s, err); > - error_free(err); > + > + migrate_error_propagate(err); > + > if (s->state == MIGRATION_STATUS_SETUP || > s->state == MIGRATION_STATUS_PRE_SWITCHOVER || > s->state == MIGRATION_STATUS_DEVICE || > @@ -588,8 +589,7 @@ void multifd_send_shutdown(void) > Error *local_err = NULL; > > if (!multifd_send_cleanup_channel(p, &local_err)) { > - migrate_set_error(migrate_get_current(), local_err); > - error_free(local_err); > + migrate_error_propagate(local_err); > } > } > > @@ -962,8 +962,7 @@ bool multifd_send_setup(void) > p->write_flags = 0; > > if (!multifd_new_send_channel_create(p, &local_err)) { > - migrate_set_error(s, local_err); > - error_free(local_err); > + migrate_error_propagate(local_err); > ret = -1; > } > } > @@ -987,8 +986,7 @@ bool multifd_send_setup(void) > > ret = multifd_send_state->ops->send_setup(p, &local_err); > if (ret) { > - migrate_set_error(s, local_err); > - error_free(local_err); > + migrate_error_propagate(local_err); > goto err; > } > assert(p->iov); > @@ -1067,8 +1065,9 @@ static void multifd_recv_terminate_threads(Error *err) > > if (err) { > MigrationState *s = migrate_get_current(); > - migrate_set_error(s, err); > - error_free(err); > + > + migrate_error_propagate(err); > + > if (s->state == MIGRATION_STATUS_SETUP || > s->state == MIGRATION_STATUS_ACTIVE) { > migrate_set_state(&s->state, s->state, > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c > index 7c9fe61041..856366072a 100644 > --- a/migration/postcopy-ram.c > +++ b/migration/postcopy-ram.c > @@ -1927,8 +1927,7 @@ postcopy_preempt_send_channel_done(MigrationState *s, > QIOChannel *ioc, Error *local_err) > { > if (local_err) { > - migrate_set_error(s, local_err); > - error_free(local_err); > + migrate_error_propagate(local_err); > } else { > migration_ioc_register_yank(ioc); > s->postcopy_qemufile_src = qemu_file_new_output(ioc); > @@ -2162,7 +2161,7 @@ static void *postcopy_listen_thread(void *opaque) > * exit depending on if postcopy-exit-on-error is true, but the > * migration cannot be recovered. > */ > - migrate_set_error(migr, local_err); > + migrate_error_propagate(error_copy(local_err)); > error_report_err(local_err); > migrate_set_state(&mis->state, mis->state, MIGRATION_STATUS_FAILED); > goto out; > diff --git a/migration/ram.c b/migration/ram.c > index 29f016cb25..1d2a47526e 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -4730,9 +4730,7 @@ static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host, > * Abort and indicate a proper reason. > */ > error_setg(&err, "RAM block '%s' resized during precopy.", rb->idstr); > - migrate_set_error(migrate_get_current(), err); > - error_free(err); > - > + migrate_error_propagate(err); > migration_cancel(); > } > > diff --git a/migration/savevm.c b/migration/savevm.c > index 638e9b364f..ab9d1e579e 100644 > --- a/migration/savevm.c > +++ b/migration/savevm.c > @@ -1125,13 +1125,12 @@ void qemu_savevm_send_open_return_path(QEMUFile *f) > int qemu_savevm_send_packaged(QEMUFile *f, const uint8_t *buf, size_t len) > { > uint32_t tmp; > - MigrationState *ms = migrate_get_current(); > Error *local_err = NULL; > > if (len > MAX_VM_CMD_PACKAGED_SIZE) { > error_setg(&local_err, "%s: Unreasonably large packaged state: %zu", > __func__, len); > - migrate_set_error(ms, local_err); > + migrate_error_propagate(error_copy(local_err)); > error_report_err(local_err); > return -1; > } > @@ -1373,7 +1372,7 @@ int qemu_savevm_state_setup(QEMUFile *f, Error **errp) > if (se->vmsd && se->vmsd->early_setup) { > ret = vmstate_save(f, se, vmdesc, errp); > if (ret) { > - migrate_set_error(ms, *errp); > + migrate_error_propagate(error_copy(*errp)); Here, we need to keep the copy because we additionally propagate to the caller. > qemu_file_set_error(f, ret); > break; > } [...]