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[99.254.121.117]) by smtp.gmail.com with ESMTPSA id o20-20020ac86d14000000b0043842dc662esm5089595qtt.4.2024.04.24.12.40.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Apr 2024 12:40:19 -0700 (PDT) Date: Wed, 24 Apr 2024 15:40:17 -0400 From: Peter Xu To: Vladimir Sementsov-Ogievskiy Cc: farosas@suse.de, eblake@redhat.com, armbru@redhat.com, pbonzini@redhat.com, qemu-devel@nongnu.org, yc-core@yandex-team.ru Subject: Re: [PATCH v2 1/2] migration: rework migrate_set_error() to migrate_report_err() Message-ID: References: <20240424174245.1237942-1-vsementsov@yandex-team.ru> <20240424174245.1237942-2-vsementsov@yandex-team.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20240424174245.1237942-2-vsementsov@yandex-team.ru> Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.668, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=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 On Wed, Apr 24, 2024 at 08:42:44PM +0300, Vladimir Sementsov-Ogievskiy wrote: > 1. Most of callers want to free the error after call. Let's help them. > > 2. Some callers log the error, some not. We also have places where we > log the stored error. Let's instead simply log every migration > error. > > 3. Some callers have to retrieve current migration state only to pass > it to migrate_set_error(). In the new helper let's get the state > automatically. > > Signed-off-by: Vladimir Sementsov-Ogievskiy > --- > migration/migration.c | 48 ++++++++++++---------------------------- > migration/migration.h | 2 +- > migration/multifd.c | 18 ++++++--------- > migration/postcopy-ram.c | 3 +-- > migration/savevm.c | 16 +++++--------- > 5 files changed, 28 insertions(+), 59 deletions(-) > > diff --git a/migration/migration.c b/migration/migration.c > index 696762bc64..806b7b080b 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -285,7 +285,7 @@ void migration_bh_schedule(QEMUBHFunc *cb, void *opaque) > void migration_cancel(const Error *error) > { > if (error) { > - migrate_set_error(current_migration, error); > + migrate_report_err(error_copy(error)); > } > if (migrate_dirty_limit()) { > qmp_cancel_vcpu_dirty_limit(false, -1, NULL); > @@ -779,13 +779,6 @@ process_incoming_migration_co(void *opaque) > } > > if (ret < 0) { > - MigrationState *s = migrate_get_current(); > - > - if (migrate_has_error(s)) { > - WITH_QEMU_LOCK_GUARD(&s->error_mutex) { > - error_report_err(s->error); > - } > - } > error_report("load of migration failed: %s", strerror(-ret)); > goto fail; > } > @@ -1402,10 +1395,6 @@ static void migrate_fd_cleanup(MigrationState *s) > MIGRATION_STATUS_CANCELLED); > } > > - if (s->error) { > - /* It is used on info migrate. We can't free it */ > - error_report_err(error_copy(s->error)); > - } > type = migration_has_failed(s) ? MIG_EVENT_PRECOPY_FAILED : > MIG_EVENT_PRECOPY_DONE; > migration_call_notifiers(s, type, NULL); > @@ -1418,12 +1407,14 @@ static void migrate_fd_cleanup_bh(void *opaque) > migrate_fd_cleanup(opaque); > } > > -void migrate_set_error(MigrationState *s, const Error *error) > +void migrate_report_err(Error *error) > { > + MigrationState *s = migrate_get_current(); Avoid passing in *s looks ok. > QEMU_LOCK_GUARD(&s->error_mutex); > if (!s->error) { > s->error = error_copy(error); I think I get your point, but then looks like this error_copy() should be removed but forgotten? I remember I had an attempt to do similarly (but only transfer the ownership): https://lore.kernel.org/qemu-devel/20230829214235.69309-3-peterx@redhat.com/ However I gave up later and I forgot why. One reason could be that I hit a use-after-free, then found that well indeed leaking an Error is much better than debugging a UAF. So maybe we simply keep it like before? If you like such change, let's just be extremely caucious. > } > + error_report_err(error); The ideal case to me is we don't trigger an error_report() all over the place. We're slightly going backward from that regard, IMHO.. Ideally I think we shouldn't dump anything to stderr, but user should always query from qmp. Thanks, -- Peter Xu