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([2a01:e0a:280:24f0:9db0:474c:ff43:9f5c]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-390e485dba4sm21940001f8f.92.2025.03.05.08.53.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 05 Mar 2025 08:53:48 -0800 (PST) Message-ID: <00b3cd87-2be1-4981-9b7a-4b92b44b7c8b@redhat.com> Date: Wed, 5 Mar 2025 17:53:48 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] migration: Always take BQL for migration_incoming_state_destroy() To: "Maciej S. Szmigiero" , Peter Xu , Fabiano Rosas Cc: Alex Williamson , Eric Blake , Markus Armbruster , =?UTF-8?Q?Daniel_P_=2E_Berrang=C3=A9?= , Avihai Horon , Joao Martins , qemu-devel@nongnu.org References: <21bb5ca337b1d5a802e697f553f37faf296b5ff4.1741193259.git.maciej.szmigiero@oracle.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: <21bb5ca337b1d5a802e697f553f37faf296b5ff4.1741193259.git.maciej.szmigiero@oracle.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_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 So that's PATCH 7 replacement. Thanks, C. On 3/5/25 17:49, Maciej S. Szmigiero wrote: > From: "Maciej S. Szmigiero" > > All callers to migration_incoming_state_destroy() other than > postcopy_ram_listen_thread() do this call with BQL held. > > Since migration_incoming_state_destroy() ultimately calls "load_cleanup" > SaveVMHandlers and it will soon call BQL-sensitive code it makes sense > to always call that function under BQL rather than to have it deal with > both cases (with BQL and without BQL). > Add the necessary bql_lock() and bql_unlock() to > postcopy_ram_listen_thread(). > > qemu_loadvm_state_main() in postcopy_ram_listen_thread() could call > "load_state" SaveVMHandlers that are expecting BQL to be held. > > In principle, the only devices that should be arriving on migration > channel serviced by postcopy_ram_listen_thread() are those that are > postcopiable and whose load handlers are safe to be called without BQL > being held. > > But nothing currently prevents the source from sending data for "unsafe" > devices which would cause trouble there. > Add a TODO comment there so it's clear that it would be good to improve > handling of such (erroneous) case in the future. > > Acked-by: Peter Xu > Signed-off-by: Maciej S. Szmigiero > --- > migration/migration.c | 13 +++++++++++++ > migration/savevm.c | 4 ++++ > 2 files changed, 17 insertions(+) > > diff --git a/migration/migration.c b/migration/migration.c > index 9e9db26667f1..0bf70ea9717d 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -402,10 +402,23 @@ void migration_incoming_state_destroy(void) > struct MigrationIncomingState *mis = migration_incoming_get_current(); > > multifd_recv_cleanup(); > + > /* > * RAM state cleanup needs to happen after multifd cleanup, because > * multifd threads can use some of its states (receivedmap). > + * The VFIO load_cleanup() implementation is BQL-sensitive. It requires > + * BQL must NOT be taken when recycling load threads, so that it won't > + * block the load threads from making progress on address space > + * modification operations. > + * > + * To make it work, we could try to not take BQL for all load_cleanup(), > + * or conditionally unlock BQL only if bql_locked() in VFIO. > + * > + * Since most existing call sites take BQL for load_cleanup(), make > + * it simple by taking BQL always as the rule, so that VFIO can unlock > + * BQL and retake unconditionally. > */ > + assert(bql_locked()); > qemu_loadvm_state_cleanup(); > > if (mis->to_src_file) { > diff --git a/migration/savevm.c b/migration/savevm.c > index 7c1aa8ad7b9d..3e86b572cfa8 100644 > --- a/migration/savevm.c > +++ b/migration/savevm.c > @@ -1986,6 +1986,8 @@ static void *postcopy_ram_listen_thread(void *opaque) > * in qemu_file, and thus we must be blocking now. > */ > qemu_file_set_blocking(f, true); > + > + /* TODO: sanity check that only postcopiable data will be loaded here */ > load_res = qemu_loadvm_state_main(f, mis); > > /* > @@ -2046,7 +2048,9 @@ static void *postcopy_ram_listen_thread(void *opaque) > * (If something broke then qemu will have to exit anyway since it's > * got a bad migration state). > */ > + bql_lock(); > migration_incoming_state_destroy(); > + bql_unlock(); > > rcu_unregister_thread(); > mis->have_listen_thread = false; >