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([2a01:e0a:280:24f0:9db0:474c:ff43:9f5c]) by smtp.gmail.com with ESMTPSA id kc19-20020a056214411300b00690d13f07f8sm2029160qvb.55.2024.03.12.06.01.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 12 Mar 2024 06:01:14 -0700 (PDT) Message-ID: <849dcde8-d20a-471c-ba59-fd1f1c60bef0@redhat.com> Date: Tue, 12 Mar 2024 14:01:11 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 10/25] migration: Add Error** argument to qemu_savevm_state_setup() Content-Language: en-US, fr To: Peter Xu , Fabiano Rosas Cc: qemu-devel@nongnu.org, Alex Williamson , Avihai Horon , =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= , Markus Armbruster , Prasad Pandit 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> From: =?UTF-8?Q?C=C3=A9dric_Le_Goater?= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=clg@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -12 X-Spam_score: -1.3 X-Spam_bar: - X-Spam_report: (-1.3 / 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, RCVD_IN_SORBS_WEB=1.5, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=no 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 3/11/24 21:10, Peter Xu wrote: > On Mon, Mar 11, 2024 at 04:03:14PM -0300, 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? >> >>> bql_lock(); >>> ret = qemu_savevm_state_setup(s->to_dst_file, &local_err); >>> bql_unlock(); >>> >>> We should fix the test instead :) Unless waiting for failover devices >>> to unplug before the save_setup handlers and not after is ok. >>> >>> commit c7e0acd5a3f8 ("migration: add new migration state wait-unplug") >>> is not clear about the justification.: >>> >>> This patch adds a new migration state called wait-unplug. It is entered >>> after the SETUP state if failover devices are present. It will transition >>> into ACTIVE once all devices were succesfully unplugged from the guest. >> >> This is not clear indeed, but to me it seems having the wait-unplug >> after setup was important. > > Finally got some time to read this code.. > > So far I didn't see an issue if it's called before the setup hooks. > Actually it looks to me it should better do that before those hooks. > > IIUC what that qemu_savevm_wait_unplug() does is waiting for all the > primary devices to be completely unplugged before moving on the migration. > > Here setup() hook, or to be explicit, the primary devices' VMSDs (if ever > existed, and if that was the concern) should have zero impact on such wait, > because the "unplug" should also contain one step to unregister those > vmsds; see the virtio_net_handle_migration_primary() where it has: > > if (failover_unplug_primary(n, dev)) { > vmstate_unregister(VMSTATE_IF(dev), qdev_get_vmsd(dev), dev); > ... > } > > So qemu_savevm_wait_unplug() looks like a pure wait function to me until > all the unplug is processed by the guest OS. And it makes some sense to me > to avoid calling setup() (which can start to hold resources, like in RAM we > create bitmaps etc to prepare for migration) before such possible long halts. I think so too now. VFIO is already sending state. > > In all cases, I guess it's still too rush to figure out a plan, meanwhile > anything proposed for either test/code changes would better get some > reviews from either Laurent or other virtio-net guys. I think I'll go > ahead the pull without the 2nd batch of patches. > >> >>> >>> >>>> ===== >>>> PS: I guess the next level in our Freestyle Concurrency video-game is to >>>> make migrate_fd_cancel() stop setting state and poking files and only >>>> set a flag that's tested in the other parts of the code. >>> >>> Is that a new item on the TODO list? >> >> Yep, I'll add it to the wiki. > > Sounds like a good thing, however let's be aware of the evils (that are > always in the details..), where there can be users/tests relying on that > "CANCELLING" state, so it can be part of the ABIs.. :-( That's a good reason to move qemu_savevm_wait_unplug() and avoid breaking the ABI. Thanks, C.