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Wed, 17 Jun 2020 18:38:11 +0000 (UTC) From: "Dr. David Alan Gilbert (git)" To: qemu-devel@nongnu.org, david@redhat.com, lvivier@redhat.com, maozhongyi@cmss.chinamobile.com, mreitz@redhat.com, pannengyuan@huawei.com Subject: [PULL 12/12] migration: fix multifd_send_pages() next channel Date: Wed, 17 Jun 2020 19:37:33 +0100 Message-Id: <20200617183733.186168-13-dgilbert@redhat.com> In-Reply-To: <20200617183733.186168-1-dgilbert@redhat.com> References: <20200617183733.186168-1-dgilbert@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=205.139.110.61; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/17 02:02:46 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: stefanha@redhat.com, quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" From: Laurent Vivier multifd_send_pages() loops around the available channels, the next channel to use between two calls to multifd_send_pages() is stored inside a local static variable, next_channel. It works well, except if the number of channels decreases between two calls to multifd_send_pages(). In this case, the loop can try to access the data of a channel that doesn't exist anymore. The problem can be triggered if we start a migration with a given number of channels and then we cancel the migration to restart it with a lower number. This ends generally with an error like: qemu-system-ppc64: .../util/qemu-thread-posix.c:77: qemu_mutex_lock_impl: Assertion `mutex->initialized' failed. This patch fixes the error by capping next_channel with the current number of channels before using it. Signed-off-by: Laurent Vivier Message-Id: <20200617113154.593233-1-lvivier@redhat.com> Reviewed-by: Juan Quintela Signed-off-by: Dr. David Alan Gilbert --- migration/multifd.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/migration/multifd.c b/migration/multifd.c index 5a3e4d0d46..d0441202aa 100644 --- a/migration/multifd.c +++ b/migration/multifd.c @@ -415,6 +415,12 @@ static int multifd_send_pages(QEMUFile *f) } qemu_sem_wait(&multifd_send_state->channels_ready); + /* + * next_channel can remain from a previous migration that was + * using more channels, so ensure it doesn't overflow if the + * limit is lower now. + */ + next_channel %= migrate_multifd_channels(); for (i = next_channel;; i = (i + 1) % migrate_multifd_channels()) { p = &multifd_send_state->params[i]; -- 2.26.2