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[184.144.111.238]) by smtp.gmail.com with ESMTPSA id j20sm10418018qtq.14.2021.07.22.10.58.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Jul 2021 10:58:47 -0700 (PDT) From: Peter Xu To: qemu-devel@nongnu.org Subject: [PATCH v3 2/5] migration: Make from_dst_file accesses thread-safe Date: Thu, 22 Jul 2021 13:58:38 -0400 Message-Id: <20210722175841.938739-3-peterx@redhat.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210722175841.938739-1-peterx@redhat.com> References: <20210722175841.938739-1-peterx@redhat.com> MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="US-ASCII" Received-SPF: pass client-ip=170.10.133.124; envelope-from=peterx@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=-1.472, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Lukas Straub , "Daniel P . Berrange" , Juan Quintela , "Dr . David Alan Gilbert" , peterx@redhat.com, Leonardo Bras Soares Passos , Eric Blake Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Accessing from_dst_file is potentially racy in current code base like below: if (s->from_dst_file) do_something(s->from_dst_file); Because from_dst_file can be reset right after the check in another thread (rp_thread). One example is migrate_fd_cancel(). Use the same qemu_file_lock to protect it too, just like to_dst_file. When it's safe to access without lock, comment it. There's one special reference in migration_thread() that can be replaced by the newly introduced rp_thread_created flag. Reported-by: Dr. David Alan Gilbert Reviewed-by: Dr. David Alan Gilbert Signed-off-by: Peter Xu --- migration/migration.c | 39 +++++++++++++++++++++++++++++---------- migration/migration.h | 8 +++++--- migration/ram.c | 1 + 3 files changed, 35 insertions(+), 13 deletions(-) diff --git a/migration/migration.c b/migration/migration.c index 21b94f75a3..b2c48b7e17 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -1879,9 +1879,11 @@ static void migrate_fd_cancel(MigrationState *s) QEMUFile *f = migrate_get_current()->to_dst_file; trace_migrate_fd_cancel(); - if (s->rp_state.from_dst_file) { - /* shutdown the rp socket, so causing the rp thread to shutdown */ - qemu_file_shutdown(s->rp_state.from_dst_file); + WITH_QEMU_LOCK_GUARD(&s->qemu_file_lock) { + if (s->rp_state.from_dst_file) { + /* shutdown the rp socket, so causing the rp thread to shutdown */ + qemu_file_shutdown(s->rp_state.from_dst_file); + } } do { @@ -2686,6 +2688,23 @@ static int migrate_handle_rp_resume_ack(MigrationState *s, uint32_t value) return 0; } +/* Release ms->rp_state.from_dst_file in a safe way */ +static void migration_release_from_dst_file(MigrationState *ms) +{ + QEMUFile *file; + + WITH_QEMU_LOCK_GUARD(&s->qemu_file_lock) { + /* + * Reset the from_dst_file pointer first before releasing it, as we + * can't block within lock section + */ + file = ms->rp_state.from_dst_file; + ms->rp_state.from_dst_file = NULL; + } + + qemu_fclose(file); +} + /* * Handles messages sent on the return path towards the source VM * @@ -2827,11 +2846,13 @@ out: * Maybe there is something we can do: it looks like a * network down issue, and we pause for a recovery. */ - qemu_fclose(rp); - ms->rp_state.from_dst_file = NULL; + migration_release_from_dst_file(ms); rp = NULL; if (postcopy_pause_return_path_thread(ms)) { - /* Reload rp, reset the rest */ + /* + * Reload rp, reset the rest. Referencing it is safe since + * it's reset only by us above, or when migration completes + */ rp = ms->rp_state.from_dst_file; ms->rp_state.error = false; goto retry; @@ -2843,8 +2864,7 @@ out: } trace_source_return_path_thread_end(); - ms->rp_state.from_dst_file = NULL; - qemu_fclose(rp); + migration_release_from_dst_file(ms); rcu_unregister_thread(); return NULL; } @@ -2852,7 +2872,6 @@ out: static int open_return_path_on_source(MigrationState *ms, bool create_thread) { - ms->rp_state.from_dst_file = qemu_file_get_return_path(ms->to_dst_file); if (!ms->rp_state.from_dst_file) { return -1; @@ -3746,7 +3765,7 @@ static void *migration_thread(void *opaque) * If we opened the return path, we need to make sure dst has it * opened as well. */ - if (s->rp_state.from_dst_file) { + if (s->rp_state.rp_thread_created) { /* Now tell the dest that it should open its end so it can reply */ qemu_savevm_send_open_return_path(s->to_dst_file); diff --git a/migration/migration.h b/migration/migration.h index c302879fad..7a5aa8c2fd 100644 --- a/migration/migration.h +++ b/migration/migration.h @@ -154,12 +154,13 @@ struct MigrationState { QemuThread thread; QEMUBH *vm_start_bh; QEMUBH *cleanup_bh; + /* Protected by qemu_file_lock */ QEMUFile *to_dst_file; QIOChannelBuffer *bioc; /* - * Protects to_dst_file pointer. We need to make sure we won't - * yield or hang during the critical section, since this lock will - * be used in OOB command handler. + * Protects to_dst_file/from_dst_file pointers. We need to make sure we + * won't yield or hang during the critical section, since this lock will be + * used in OOB command handler. */ QemuMutex qemu_file_lock; @@ -192,6 +193,7 @@ struct MigrationState { /* State related to return path */ struct { + /* Protected by qemu_file_lock */ QEMUFile *from_dst_file; QemuThread rp_thread; bool error; diff --git a/migration/ram.c b/migration/ram.c index b5fc454b2f..f728f5072f 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -4012,6 +4012,7 @@ static void ram_dirty_bitmap_reload_notify(MigrationState *s) int ram_dirty_bitmap_reload(MigrationState *s, RAMBlock *block) { int ret = -EINVAL; + /* from_dst_file is always valid because we're within rp_thread */ QEMUFile *file = s->rp_state.from_dst_file; unsigned long *le_bitmap, nbits = block->used_length >> TARGET_PAGE_BITS; uint64_t local_size = DIV_ROUND_UP(nbits, 8); -- 2.31.1