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([2a01:e0a:165:d60:bbdd:3c5e:7d8b:3f72]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38058b1c4d8sm1453895f8f.2.2024.10.25.05.50.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 25 Oct 2024 05:50:36 -0700 (PDT) Message-ID: Date: Fri, 25 Oct 2024 14:50:36 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 8/8] migration: Protect updates to current_migration with a mutex To: Peter Xu , qemu-devel@nongnu.org Cc: Avihai Horon , Fabiano Rosas , Alex Williamson References: <20241024213056.1395400-1-peterx@redhat.com> <20241024213056.1395400-9-peterx@redhat.com> Content-Language: en-US, fr From: =?UTF-8?Q?C=C3=A9dric_Le_Goater?= Autocrypt: addr=clg@redhat.com; keydata= xsFNBFu8o3UBEADP+oJVJaWm5vzZa/iLgpBAuzxSmNYhURZH+guITvSySk30YWfLYGBWQgeo 8NzNXBY3cH7JX3/a0jzmhDc0U61qFxVgrPqs1PQOjp7yRSFuDAnjtRqNvWkvlnRWLFq4+U5t yzYe4SFMjFb6Oc0xkQmaK2flmiJNnnxPttYwKBPd98WfXMmjwAv7QfwW+OL3VlTPADgzkcqj 53bfZ4VblAQrq6Ctbtu7JuUGAxSIL3XqeQlAwwLTfFGrmpY7MroE7n9Rl+hy/kuIrb/TO8n0 ZxYXvvhT7OmRKvbYuc5Jze6o7op/bJHlufY+AquYQ4dPxjPPVUT/DLiUYJ3oVBWFYNbzfOrV RxEwNuRbycttMiZWxgflsQoHF06q/2l4ttS3zsV4TDZudMq0TbCH/uJFPFsbHUN91qwwaN/+ gy1j7o6aWMz+Ib3O9dK2M/j/O/Ube95mdCqN4N/uSnDlca3YDEWrV9jO1mUS/ndOkjxa34ia 70FjwiSQAsyIwqbRO3CGmiOJqDa9qNvd2TJgAaS2WCw/TlBALjVQ7AyoPEoBPj31K74Wc4GS Rm+FSch32ei61yFu6ACdZ12i5Edt+To+hkElzjt6db/UgRUeKfzlMB7PodK7o8NBD8outJGS tsL2GRX24QvvBuusJdMiLGpNz3uqyqwzC5w0Fd34E6G94806fwARAQABzSJDw6lkcmljIExl IEdvYXRlciA8Y2xnQHJlZGhhdC5jb20+wsGRBBMBCAA7FiEEoPZlSPBIlev+awtgUaNDx8/7 7KEFAmTLlVECGwMFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgkQUaNDx8/77KG0eg// S0zIzTcxkrwJ/9XgdcvVTnXLVF9V4/tZPfB7sCp8rpDCEseU6O0TkOVFoGWM39sEMiQBSvyY lHrP7p7E/JYQNNLh441MfaX8RJ5Ul3btluLapm8oHp/vbHKV2IhLcpNCfAqaQKdfk8yazYhh EdxTBlzxPcu+78uE5fF4wusmtutK0JG0sAgq0mHFZX7qKG6LIbdLdaQalZ8CCFMKUhLptW71 xe+aNrn7hScBoOj2kTDRgf9CE7svmjGToJzUxgeh9mIkxAxTu7XU+8lmL28j2L5uNuDOq9vl hM30OT+pfHmyPLtLK8+GXfFDxjea5hZLF+2yolE/ATQFt9AmOmXC+YayrcO2ZvdnKExZS1o8 VUKpZgRnkwMUUReaF/mTauRQGLuS4lDcI4DrARPyLGNbvYlpmJWnGRWCDguQ/LBPpbG7djoy k3NlvoeA757c4DgCzggViqLm0Bae320qEc6z9o0X0ePqSU2f7vcuWN49Uhox5kM5L86DzjEQ RHXndoJkeL8LmHx8DM+kx4aZt0zVfCHwmKTkSTQoAQakLpLte7tWXIio9ZKhUGPv/eHxXEoS 0rOOAZ6np1U/xNR82QbF9qr9TrTVI3GtVe7Vxmff+qoSAxJiZQCo5kt0YlWwti2fFI4xvkOi V7lyhOA3+/3oRKpZYQ86Frlo61HU3r6d9wzOwU0EW7yjdQEQALyDNNMw/08/fsyWEWjfqVhW pOOrX2h+z4q0lOHkjxi/FRIRLfXeZjFfNQNLSoL8j1y2rQOs1j1g+NV3K5hrZYYcMs0xhmrZ KXAHjjDx7FW3sG3jcGjFW5Xk4olTrZwFsZVUcP8XZlArLmkAX3UyrrXEWPSBJCXxDIW1hzwp bV/nVbo/K9XBptT/wPd+RPiOTIIRptjypGY+S23HYBDND3mtfTz/uY0Jytaio9GETj+fFis6 TxFjjbZNUxKpwftu/4RimZ7qL+uM1rG1lLWc9SPtFxRQ8uLvLOUFB1AqHixBcx7LIXSKZEFU CSLB2AE4wXQkJbApye48qnZ09zc929df5gU6hjgqV9Gk1rIfHxvTsYltA1jWalySEScmr0iS YBZjw8Nbd7SxeomAxzBv2l1Fk8fPzR7M616dtb3Z3HLjyvwAwxtfGD7VnvINPbzyibbe9c6g LxYCr23c2Ry0UfFXh6UKD83d5ybqnXrEJ5n/t1+TLGCYGzF2erVYGkQrReJe8Mld3iGVldB7 JhuAU1+d88NS3aBpNF6TbGXqlXGF6Yua6n1cOY2Yb4lO/mDKgjXd3aviqlwVlodC8AwI0Sdu jWryzL5/AGEU2sIDQCHuv1QgzmKwhE58d475KdVX/3Vt5I9kTXpvEpfW18TjlFkdHGESM/Jx IqVsqvhAJkalABEBAAHCwV8EGAECAAkFAlu8o3UCGwwACgkQUaNDx8/77KEhwg//WqVopd5k 8hQb9VVdk6RQOCTfo6wHhEqgjbXQGlaxKHoXywEQBi8eULbeMQf5l4+tHJWBxswQ93IHBQjK yKyNr4FXseUI5O20XVNYDJZUrhA4yn0e/Af0IX25d94HXQ5sMTWr1qlSK6Zu79lbH3R57w9j hQm9emQEp785ui3A5U2Lqp6nWYWXz0eUZ0Tad2zC71Gg9VazU9MXyWn749s0nXbVLcLS0yop s302Gf3ZmtgfXTX/W+M25hiVRRKCH88yr6it+OMJBUndQVAA/fE9hYom6t/zqA248j0QAV/p LHH3hSirE1mv+7jpQnhMvatrwUpeXrOiEw1nHzWCqOJUZ4SY+HmGFW0YirWV2mYKoaGO2YBU wYF7O9TI3GEEgRMBIRT98fHa0NPwtlTktVISl73LpgVscdW8yg9Gc82oe8FzU1uHjU8b10lU XOMHpqDDEV9//r4ZhkKZ9C4O+YZcTFu+mvAY3GlqivBNkmYsHYSlFsbxc37E1HpTEaSWsGfA HQoPn9qrDJgsgcbBVc1gkUT6hnxShKPp4PlsZVMNjvPAnr5TEBgHkk54HQRhhwcYv1T2QumQ izDiU6iOrUzBThaMhZO3i927SG2DwWDVzZltKrCMD1aMPvb3NU8FOYRhNmIFR3fcalYr+9gD uVKe8BVz4atMOoktmt0GWTOC8P4= In-Reply-To: <20241024213056.1395400-9-peterx@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=clg@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.454, 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_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 10/24/24 23:30, Peter Xu wrote: > Introduce migration_mutex, protecting concurrent updates to > current_migration. > > In reality, most of the exported migration functions are safe to access > migration objects on capabilities, etc., e.g. many of the code is invoked > within migration thread via different hooks (e.g., precopy notifier, > vmstate handler hooks, etc.). > > So literally the mutex so far only makes sure below two APIs that are prone > to accessing freed current_migration: > > migration_is_running() > migration_file_set_error() > > Then we'll need to take the mutex too when init/free the migration object. we should also drop : static void vfio_set_migration_error(int ret) { if (migration_is_running()) { migration_file_set_error(ret, NULL); } } and use directly migration_file_set_error(). > > Signed-off-by: Peter Xu > --- > migration/migration.h | 3 +++ > migration/migration.c | 43 +++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 46 insertions(+) > > diff --git a/migration/migration.h b/migration/migration.h > index 9fa26ab06a..05edcf0c49 100644 > --- a/migration/migration.h > +++ b/migration/migration.h > @@ -473,6 +473,9 @@ struct MigrationState { > bool rdma_migration; > }; > > +extern QemuMutex migration_mutex; > +#define QEMU_MIGRATION_LOCK_GUARD() QEMU_LOCK_GUARD(&migration_mutex) > + Why are these definitions exported ? Thanks, C. > void migrate_set_state(MigrationStatus *state, MigrationStatus old_state, > MigrationStatus new_state); > > diff --git a/migration/migration.c b/migration/migration.c > index 127b01734d..ef044968df 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -97,6 +97,14 @@ enum mig_rp_message_type { > migrations at once. For now we don't need to add > dynamic creation of migration */ > > +/* > + * Protects current_migration below. Must be hold when using migration > + * exported functions unless the caller knows it won't get freed. For > + * example, when in the context of migration_thread() it's safe to access > + * current_migration without the mutex, because the thread holds one extra > + * refcount of the object, so it literally pins the object in-memory. > + */ > +QemuMutex migration_mutex; > static MigrationState *current_migration; > static MigrationIncomingState *current_incoming; > > @@ -110,6 +118,17 @@ static void migrate_fd_cancel(MigrationState *s); > static bool close_return_path_on_source(MigrationState *s); > static void migration_completion_end(MigrationState *s); > > +/* > + * This is explicitly done without migration_object_init(), because it may > + * start to use this lock already when instance_init() of the object. The > + * mutex is alive for the whole lifecycle of QEMU, so it's always usable > + * and never destroyed. > + */ > +static void __attribute__((constructor)) migration_mutex_init(void) > +{ > + qemu_mutex_init(&migration_mutex); > +} > + > static void migration_downtime_start(MigrationState *s) > { > trace_vmstate_downtime_checkpoint("src-downtime-start"); > @@ -336,6 +355,14 @@ void migration_shutdown(void) > * stop the migration using this structure > */ > migration_cancel(NULL); > + /* > + * Release the refcount from the main thread. It means it can be freed > + * here if migration thread is not running. > + * > + * NOTE: we don't need QEMU_MIGRATION_LOCK_GUARD() on this access > + * because we're sure there's one refcount. The lock will be taken in > + * finalize() if it triggers, so we can't take it here anyway. > + */ > object_unref(OBJECT(current_migration)); > > /* > @@ -1118,8 +1145,14 @@ void migrate_send_rp_resume_ack(MigrationIncomingState *mis, uint32_t value) > > bool migration_is_running(void) > { > + QEMU_MIGRATION_LOCK_GUARD(); > + > MigrationState *s = current_migration; > > + if (!s) { > + return false; > + } > + > switch (s->state) { > case MIGRATION_STATUS_ACTIVE: > case MIGRATION_STATUS_POSTCOPY_ACTIVE: > @@ -3029,8 +3062,14 @@ static MigThrError postcopy_pause(MigrationState *s) > > void migration_file_set_error(int ret, Error *err) > { > + QEMU_MIGRATION_LOCK_GUARD(); > + > MigrationState *s = current_migration; > > + if (!s) { > + return; > + } > + > WITH_QEMU_LOCK_GUARD(&s->qemu_file_lock) { > if (s->to_dst_file) { > qemu_file_set_error_obj(s->to_dst_file, ret, err); > @@ -3835,6 +3874,8 @@ static void migration_instance_finalize(Object *obj) > { > MigrationState *ms = MIGRATION_OBJ(obj); > > + QEMU_MIGRATION_LOCK_GUARD(); > + > qemu_mutex_destroy(&ms->error_mutex); > qemu_mutex_destroy(&ms->qemu_file_lock); > qemu_sem_destroy(&ms->wait_unplug_sem); > @@ -3858,6 +3899,8 @@ static void migration_instance_init(Object *obj) > { > MigrationState *ms = MIGRATION_OBJ(obj); > > + QEMU_MIGRATION_LOCK_GUARD(); > + > /* > * There can only be one migration object globally. Keep a record of > * the pointer in current_migration, which will be reset after the