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[99.254.121.117]) by smtp.gmail.com with ESMTPSA id r6-20020a0cf606000000b0069046d929a3sm3708693qvm.145.2024.03.12.08.19.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 12 Mar 2024 08:19:00 -0700 (PDT) Date: Tue, 12 Mar 2024 11:18:58 -0400 From: Peter Xu To: Fabiano Rosas Cc: =?utf-8?Q?C=C3=A9dric?= Le Goater , qemu-devel@nongnu.org, Alex Williamson , Avihai Horon , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Markus Armbruster , Prasad Pandit Subject: Re: [PATCH v4 10/25] migration: Add Error** argument to qemu_savevm_state_setup() Message-ID: References: <20240306133441.2351700-1-clg@redhat.com> <20240306133441.2351700-11-clg@redhat.com> <87plw44wps.fsf@suse.de> <1566715b-a9a5-4df6-8e64-f4f912e2ea2f@redhat.com> <87le6omw0d.fsf@suse.de> <9071affc-ffb5-435a-99d1-ca829703e31b@redhat.com> <8ba5dba7-1849-46ff-b708-a9caac66be27@redhat.com> <874jdbmst4.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <874jdbmst4.fsf@suse.de> 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=-0.687, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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 Tue, Mar 12, 2024 at 11:24:39AM -0300, Fabiano Rosas wrote: > Cédric Le Goater writes: > > > On 3/12/24 14:34, Cédric Le Goater wrote: > >> On 3/12/24 13:32, Cédric Le Goater wrote: > >>> On 3/11/24 20:03, Fabiano Rosas wrote: > >>>> Cédric Le Goater writes: > >>>> > >>>>> On 3/8/24 15:36, Fabiano Rosas wrote: > >>>>>> Cédric Le Goater writes: > >>>>>> > >>>>>>> This prepares ground for the changes coming next which add an Error** > >>>>>>> argument to the .save_setup() handler. Callers of qemu_savevm_state_setup() > >>>>>>> now handle the error and fail earlier setting the migration state from > >>>>>>> MIGRATION_STATUS_SETUP to MIGRATION_STATUS_FAILED. > >>>>>>> > >>>>>>> In qemu_savevm_state(), move the cleanup to preserve the error > >>>>>>> reported by .save_setup() handlers. > >>>>>>> > >>>>>>> Since the previous behavior was to ignore errors at this step of > >>>>>>> migration, this change should be examined closely to check that > >>>>>>> cleanups are still correctly done. > >>>>>>> > >>>>>>> Signed-off-by: Cédric Le Goater > >>>>>>> --- > >>>>>>> > >>>>>>>    Changes in v4: > >>>>>>>    - Merged cleanup change in qemu_savevm_state() > >>>>>>>    Changes in v3: > >>>>>>>    - Set migration state to MIGRATION_STATUS_FAILED > >>>>>>>    - Fixed error handling to be done under lock in bg_migration_thread() > >>>>>>>    - Made sure an error is always set in case of failure in > >>>>>>>      qemu_savevm_state_setup() > >>>>>>>    migration/savevm.h    |  2 +- > >>>>>>>    migration/migration.c | 27 ++++++++++++++++++++++++--- > >>>>>>>    migration/savevm.c    | 26 +++++++++++++++----------- > >>>>>>>    3 files changed, 40 insertions(+), 15 deletions(-) > >>>>>>> > >>>>>>> diff --git a/migration/savevm.h b/migration/savevm.h > >>>>>>> index 74669733dd63a080b765866c703234a5c4939223..9ec96a995c93a42aad621595f0ed58596c532328 100644 > >>>>>>> --- a/migration/savevm.h > >>>>>>> +++ b/migration/savevm.h > >>>>>>> @@ -32,7 +32,7 @@ > >>>>>>>    bool qemu_savevm_state_blocked(Error **errp); > >>>>>>>    void qemu_savevm_non_migratable_list(strList **reasons); > >>>>>>>    int qemu_savevm_state_prepare(Error **errp); > >>>>>>> -void qemu_savevm_state_setup(QEMUFile *f); > >>>>>>> +int qemu_savevm_state_setup(QEMUFile *f, Error **errp); > >>>>>>>    bool qemu_savevm_state_guest_unplug_pending(void); > >>>>>>>    int qemu_savevm_state_resume_prepare(MigrationState *s); > >>>>>>>    void qemu_savevm_state_header(QEMUFile *f); > >>>>>>> diff --git a/migration/migration.c b/migration/migration.c > >>>>>>> index a49fcd53ee19df1ce0182bc99d7e064968f0317b..6d1544224e96f5edfe56939a9c8395d88ef29581 100644 > >>>>>>> --- a/migration/migration.c > >>>>>>> +++ b/migration/migration.c > >>>>>>> @@ -3408,6 +3408,8 @@ static void *migration_thread(void *opaque) > >>>>>>>        int64_t setup_start = qemu_clock_get_ms(QEMU_CLOCK_HOST); > >>>>>>>        MigThrError thr_error; > >>>>>>>        bool urgent = false; > >>>>>>> +    Error *local_err = NULL; > >>>>>>> +    int ret; > >>>>>>>        thread = migration_threads_add("live_migration", qemu_get_thread_id()); > >>>>>>> @@ -3451,9 +3453,17 @@ static void *migration_thread(void *opaque) > >>>>>>>        } > >>>>>>>        bql_lock(); > >>>>>>> -    qemu_savevm_state_setup(s->to_dst_file); > >>>>>>> +    ret = qemu_savevm_state_setup(s->to_dst_file, &local_err); > >>>>>>>        bql_unlock(); > >>>>>>> +    if (ret) { > >>>>>>> +        migrate_set_error(s, local_err); > >>>>>>> +        error_free(local_err); > >>>>>>> +        migrate_set_state(&s->state, MIGRATION_STATUS_SETUP, > >>>>>>> +                          MIGRATION_STATUS_FAILED); > >>>>>>> +        goto out; > >>>>>>> +     } > >>>>>>> + > >>>>>>>        qemu_savevm_wait_unplug(s, MIGRATION_STATUS_SETUP, > >>>>>>>                                   MIGRATION_STATUS_ACTIVE); > >>>>>> > >>>>>> This^ should be before the new block it seems: > >>>>>> > >>>>>> GOOD: > >>>>>> migrate_set_state new state setup > >>>>>> migrate_set_state new state wait-unplug > >>>>>> migrate_fd_cancel > >>>>>> migrate_set_state new state cancelling > >>>>>> migrate_fd_cleanup > >>>>>> migrate_set_state new state cancelled > >>>>>> migrate_fd_cancel > >>>>>> ok 1 /x86_64/failover-virtio-net/migrate/abort/wait-unplug > >>>>>> > >>>>>> BAD: > >>>>>> migrate_set_state new state setup > >>>>>> migrate_fd_cancel > >>>>>> migrate_set_state new state cancelling > >>>>>> migrate_fd_cleanup > >>>>>> migrate_set_state new state cancelled > >>>>>> qemu-system-x86_64: ram_save_setup failed: Input/output error > >>>>>> ** > >>>>>> ERROR:../tests/qtest/virtio-net-failover.c:1203:test_migrate_abort_wait_unplug: > >>>>>> assertion failed (status == "cancelling"): ("cancelled" == "cancelling") > >>>>>> > >>>>>> Otherwise migration_iteration_finish() will schedule the cleanup BH and > >>>>>> that will run concurrently with migrate_fd_cancel() issued by the test > >>>>>> and bad things happens. > >>>>> > >>>>> This hack makes things work : > >>>>> > >>>>> @@ -3452,6 +3452,9 @@ static void *migration_thread(void *opaq > >>>>>            qemu_savevm_send_colo_enable(s->to_dst_file); > >>>>>        } > >>>>> +    qemu_savevm_wait_unplug(s, MIGRATION_STATUS_SETUP, > >>>>> +                            MIGRATION_STATUS_SETUP); > >>>>> + > >>>> > >>>> Why move it all the way up here? Has moving the wait_unplug before the > >>>> 'if (ret)' block not worked for you? > >>> > >>> We could be sleeping while holding the BQL. It looked wrong. > >> > >> Sorry wrong answer. Yes I can try moving it before the 'if (ret)' block. > >> I can reproduce easily with an x86 guest running on PPC64. > > > > That works just the same. > > > > Peter, Fabiano, > > > > What would you prefer ? > > > > 1. move qemu_savevm_wait_unplug() before qemu_savevm_state_setup(), > > means one new patch. > > Is there a point to this except "because we can"? Honest question, I > might have missed the motivation. My previous point was, it avoids holding the resources (that will be allocated in setup() routines) while we know we can wait for a long time. But then I found that the ordering is indeed needed at least if we don't change migrate_set_state() first - it is the only place we set the status to START (which I overlooked, sorry)... IMHO the function is not well designed; the state update of the next stage should not reside in a function to wait for failover primary devices conditionally. It's a bit of a mess. > > Also a couple of points: > > - The current version of this proposal seems it will lose the transition > from SETUP->ACTIVE no? As in, after qemu_savevm_state_setup, there's > nothing changing the state to ACTIVE anymore. > > - You also need to change the bg migration path. > > > > > 2. leave qemu_savevm_wait_unplug() after qemu_savevm_state_setup() > > and handle state_setup() errors after waiting. means an update > > of this patch. > > I vote for this. This failover feature is a pretty complex one, let's > not risk changing the behavior for no good reason. Just look at the > amount of head-banging going on in these threads: > > https://patchwork.ozlabs.org/project/qemu-devel/cover/20181025140631.634922-1-sameeh@daynix.com/ > https://www.mail-archive.com/qemu-devel@nongnu.org/msg609296.html Do we know who is consuming this feature? Now VFIO allows a migration to happen without this trick. I'm wondering whether all relevant NICs can also support VFIO migrations in the future, then we can drop this tricky feature for good. -- Peter Xu