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Tue, 8 Oct 2024 21:36:55 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id ZFwQFfelBWcrHAAAD6G6ig (envelope-from ); Tue, 08 Oct 2024 21:36:55 +0000 From: Fabiano Rosas To: Elena Ufimtseva Cc: qemu-devel@nongnu.org, Peter Xu , Peter Maydell , qemu-stable@nongnu.org Subject: Re: [PATCH 2/2] migration/multifd: Fix rb->receivedmap cleanup race In-Reply-To: References: <20240913220542.18305-1-farosas@suse.de> <20240913220542.18305-3-farosas@suse.de> Date: Tue, 08 Oct 2024 18:36:53 -0300 Message-ID: <874j5mtgy2.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-0.999]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; ARC_NA(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; MIME_TRACE(0.00)[0:+]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; TO_DN_SOME(0.00)[]; FREEMAIL_TO(0.00)[gmail.com]; RCVD_TLS_ALL(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; MISSING_XM_UA(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_FIVE(0.00)[5]; RCVD_COUNT_TWO(0.00)[2]; RCVD_VIA_SMTP_AUTH(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,suse.de:mid] Received-SPF: pass client-ip=195.135.223.131; envelope-from=farosas@suse.de; helo=smtp-out2.suse.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, 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 Elena Ufimtseva writes: > On Fri, Sep 13, 2024 at 3:07=E2=80=AFPM Fabiano Rosas w= rote: > >> Fix a segmentation fault in multifd when rb->receivedmap is cleared >> too early. >> >> After commit 5ef7e26bdb ("migration/multifd: solve zero page causing >> multiple page faults"), multifd started using the rb->receivedmap >> bitmap, which belongs to ram.c and is initialized and *freed* from the >> ram SaveVMHandlers. >> >> Multifd threads are live until migration_incoming_state_destroy(), >> which is called after qemu_loadvm_state_cleanup(), leading to a crash >> when accessing rb->receivedmap. >> >> process_incoming_migration_co() ... >> qemu_loadvm_state() multifd_nocomp_recv() >> qemu_loadvm_state_cleanup() ramblock_recv_bitmap_set_offset= () >> rb->receivedmap =3D NULL set_bit_atomic(..., >> rb->receivedmap) >> ... >> migration_incoming_state_destroy() >> multifd_recv_cleanup() >> multifd_recv_terminate_threads(NULL) >> >> Move the loadvm cleanup into migration_incoming_state_destroy(), after >> multifd_recv_cleanup() to ensure multifd thread have already exited >> when rb->receivedmap is cleared. >> >> The have_listen_thread logic can now be removed because its purpose >> was to delay cleanup until postcopy_ram_listen_thread() had finished. >> >> CC: qemu-stable@nongnu.org >> Fixes: 5ef7e26bdb ("migration/multifd: solve zero page causing multiple >> page faults") >> Signed-off-by: Fabiano Rosas >> --- >> migration/migration.c | 1 + >> migration/migration.h | 1 - >> migration/savevm.c | 9 --------- >> 3 files changed, 1 insertion(+), 10 deletions(-) >> >> diff --git a/migration/migration.c b/migration/migration.c >> index 3dea06d577..b190a574b1 100644 >> --- a/migration/migration.c >> +++ b/migration/migration.c >> @@ -378,6 +378,7 @@ void migration_incoming_state_destroy(void) >> struct MigrationIncomingState *mis =3D migration_incoming_get_curre= nt(); >> >> multifd_recv_cleanup(); >> + qemu_loadvm_state_cleanup(); >> >> if (mis->to_src_file) { >> /* Tell source that we are done */ >> diff --git a/migration/migration.h b/migration/migration.h >> index 38aa1402d5..20b0a5b66e 100644 >> --- a/migration/migration.h >> +++ b/migration/migration.h >> @@ -101,7 +101,6 @@ struct MigrationIncomingState { >> /* Set this when we want the fault thread to quit */ >> bool fault_thread_quit; >> >> - bool have_listen_thread; >> QemuThread listen_thread; >> >> /* For the kernel to send us notifications */ >> diff --git a/migration/savevm.c b/migration/savevm.c >> index d0759694fd..532ee5e4b0 100644 >> --- a/migration/savevm.c >> +++ b/migration/savevm.c >> @@ -2076,10 +2076,8 @@ static void *postcopy_ram_listen_thread(void >> *opaque) >> * got a bad migration state). >> */ >> migration_incoming_state_destroy(); >> - qemu_loadvm_state_cleanup(); >> >> rcu_unregister_thread(); >> - mis->have_listen_thread =3D false; >> postcopy_state_set(POSTCOPY_INCOMING_END); >> >> object_unref(OBJECT(migr)); >> @@ -2130,7 +2128,6 @@ static int >> loadvm_postcopy_handle_listen(MigrationIncomingState *mis) >> return -1; >> } >> >> - mis->have_listen_thread =3D true; >> postcopy_thread_create(mis, &mis->listen_thread, "mig/dst/listen", >> postcopy_ram_listen_thread, >> QEMU_THREAD_DETACHED); >> trace_loadvm_postcopy_handle_listen("return"); >> @@ -2978,11 +2975,6 @@ int qemu_loadvm_state(QEMUFile *f) >> >> trace_qemu_loadvm_state_post_main(ret); >> >> - if (mis->have_listen_thread) { >> - /* Listen thread still going, can't clean up yet */ >> - return ret; >> - } >> - >> if (ret =3D=3D 0) { >> ret =3D qemu_file_get_error(f); >> } >> @@ -3022,7 +3014,6 @@ int qemu_loadvm_state(QEMUFile *f) >> } >> } >> >> - qemu_loadvm_state_cleanup(); >> cpu_synchronize_all_post_init(); >> > > > Hi Fabiano Hi, sorry for the delay. > > I have a question. By removing qemu_loadvm_state_cleanup() here, the > failure path that ends up with exit(EXIT_FAILURE) > in process_incoming_migration_co() end up not calling the > qemu_loadvm_state_cleanup(). I am not sure how this is important since > there is exit, but the > vfio, for example, will not call the VF reset. In the fail label, migration_incoming_state_destroy() is called right before the exit block. > > Another more general question is why destination Qemu has to terminate > there if there was an error detected during live migration? > Could just failing the migration and leave destination running be a more > expected scenario? After failure to load, the destination VM is not really usable, so terminating it seems ok. This was changed with the addition of mis->exit_on_error in dbea1c89da ("qapi: introduce exit-on-error parameter for migrate-incoming"). We still exit on error by default, but allow the user to modify the behavior to allow management applications to collect the error or inspect the VM. > > Thank you! > > return ret; >> -- >> 2.35.3 >> >> >>