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([2a01:e0a:165:d60:bbdd:3c5e:7d8b:3f72]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4316f5cc88esm91280685e9.46.2024.10.22.09.11.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 22 Oct 2024 09:11:20 -0700 (PDT) Message-ID: <519f0ed8-5346-463b-979a-a4c6f4c38a8b@redhat.com> Date: Tue, 22 Oct 2024 18:11:19 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] migration: Make all helpers in misc.h safe to use without migration To: Peter Xu , qemu-devel@nongnu.org Cc: Avihai Horon , Alex Williamson , Fabiano Rosas , "Dr . David Alan Gilbert" References: <20241022160720.1013543-1-peterx@redhat.com> <20241022160720.1013543-2-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: <20241022160720.1013543-2-peterx@redhat.com> 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: -42 X-Spam_score: -4.3 X-Spam_bar: ---- X-Spam_report: (-4.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.519, 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_H2=-1.697, 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 On 10/22/24 18:07, Peter Xu wrote: > Migration object can be freed before some other device codes run, while we > do have a bunch of migration helpers exported in migration/misc.h that > logically can be invoked at any time of QEMU, even during destruction of a > VM. > > Make all these functions safe to be called, especially, not crashing after > the migration object is freed. > > Add a rich comment in the header explaining how to guarantee thread safe on > using these functions, and we choose BQL because fundamentally that's how > it's working now. We can move to other things (e.g. RCU) whenever > necessary in the future but it's an overkill if we have BQL anyway in > most/all existing callers. > > When at it, update some comments, e.g. migrate_announce_params() is While ? > exported from options.c now. > > Cc: Cédric Le Goater > Cc: Avihai Horon > Cc: Fabiano Rosas > Cc: Dr. David Alan Gilbert > Signed-off-by: Peter Xu Reviewed-by: Cédric Le Goater Thanks, C. > --- > include/migration/misc.h | 33 ++++++++++++++++++++++++++++----- > migration/migration.c | 22 +++++++++++++++++++++- > 2 files changed, 49 insertions(+), 6 deletions(-) > > diff --git a/include/migration/misc.h b/include/migration/misc.h > index bfadc5613b..8d6812b8c7 100644 > --- a/include/migration/misc.h > +++ b/include/migration/misc.h > @@ -19,8 +19,26 @@ > #include "qapi/qapi-types-net.h" > #include "migration/client-options.h" > > -/* migration/ram.c */ > +/* > + * Misc migration functions exported to be used in QEMU generic system > + * code outside migration/. > + * > + * By default, BQL is required to use below functions to avoid race > + * conditions (e.g. concurrent free of the migration object). It's > + * caller's responsibility to make sure it's thread safe otherwise when > + * below helpers are used without BQL held. > + * > + * One example of the special case is migration_thread(), who will take a > + * refcount of the migration object. The refcount will make sure the > + * migration object will not be freed concurrently when accessing through > + * below helpers. > + * > + * When unsure, always take BQL first before using the helpers. > + */ > > +/* > + * migration/ram.c > + */ > typedef enum PrecopyNotifyReason { > PRECOPY_NOTIFY_SETUP = 0, > PRECOPY_NOTIFY_BEFORE_BITMAP_SYNC = 1, > @@ -43,14 +61,19 @@ void ram_mig_init(void); > void qemu_guest_free_page_hint(void *addr, size_t len); > bool migrate_ram_is_ignored(RAMBlock *block); > > -/* migration/block.c */ > - > +/* > + * migration/options.c > + */ > AnnounceParameters *migrate_announce_params(void); > -/* migration/savevm.c */ > > +/* > + * migration/savevm.c > + */ > void dump_vmstate_json_to_file(FILE *out_fp); > > -/* migration/migration.c */ > +/* > + * migration/migration.c > + */ > void migration_object_init(void); > void migration_shutdown(void); > bool migration_is_idle(void); > diff --git a/migration/migration.c b/migration/migration.c > index bcb735869b..27341eed50 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -1121,6 +1121,10 @@ bool migration_is_setup_or_active(void) > { > MigrationState *s = current_migration; > > + if (!s) { > + return false; > + } > + > switch (s->state) { > case MIGRATION_STATUS_ACTIVE: > case MIGRATION_STATUS_POSTCOPY_ACTIVE: > @@ -1136,7 +1140,6 @@ bool migration_is_setup_or_active(void) > > default: > return false; > - > } > } > > @@ -1685,6 +1688,10 @@ bool migration_is_active(void) > { > MigrationState *s = current_migration; > > + if (!s) { > + return false; > + } > + > return (s->state == MIGRATION_STATUS_ACTIVE || > s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE); > } > @@ -1693,6 +1700,10 @@ bool migration_is_device(void) > { > MigrationState *s = current_migration; > > + if (!s) { > + return false; > + } > + > return s->state == MIGRATION_STATUS_DEVICE; > } > > @@ -1700,6 +1711,11 @@ bool migration_thread_is_self(void) > { > MigrationState *s = current_migration; > > + /* If no migration object, must not be the migration thread */ > + if (!s) { > + return false; > + } > + > return qemu_thread_is_self(&s->thread); > } > > @@ -3077,6 +3093,10 @@ void migration_file_set_error(int ret, Error *err) > { > 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);