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bh=8sTZ2tLPTwfI8PVRQNhye5uLdMdQcsdyAavf636xeAI=; b=ANwOSRP8CeC7/E+V8ze52KNSblwBdUeZYykcM+051XVMnZc3JSlwKeRgETpUhK0nIUTgyd g2v27gpWrc4J662k2+s4RVRKg7kZXA/Rc6UWWWKf8NL7nzLr27jVv8uJCejjPbJ1BEWwql DDpDp8mZuy0BcICy27ASpMDlhT3drhE= X-MC-Unique: BWnpH5dGP1OECfgnGdByKg-1 From: Juan Quintela To: qemu-devel@nongnu.org Cc: Michael Tokarev , =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= , David Hildenbrand , Laurent Vivier , Juan Quintela , Paolo Bonzini , =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= , Peter Xu , Stefan Hajnoczi , "Dr. David Alan Gilbert" , Thomas Huth , qemu-block@nongnu.org, qemu-trivial@nongnu.org, =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , Fam Zheng Subject: [PULL 10/30] migration: Fix possible infinite loop of ram save process Date: Tue, 15 Nov 2022 16:34:54 +0100 Message-Id: <20221115153514.28003-11-quintela@redhat.com> In-Reply-To: <20221115153514.28003-1-quintela@redhat.com> References: <20221115153514.28003-1-quintela@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=quintela@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1668527920741100001 Content-Type: text/plain; charset="utf-8" From: Peter Xu When starting ram saving procedure (especially at the completion phase), always set last_seen_block to non-NULL to make sure we can always correctly detect the case where "we've migrated all the dirty pages". Then we'll guarantee both last_seen_block and pss.block will be valid always before the loop starts. See the comment in the code for some details. Reviewed-by: Dr. David Alan Gilbert Signed-off-by: Peter Xu Reviewed-by: Juan Quintela Signed-off-by: Juan Quintela --- migration/ram.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/migration/ram.c b/migration/ram.c index bb4f08bfed..c0f5d6d287 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -2574,14 +2574,22 @@ static int ram_find_and_save_block(RAMState *rs) return pages; } =20 + /* + * Always keep last_seen_block/last_page valid during this procedure, + * because find_dirty_block() relies on these values (e.g., we compare + * last_seen_block with pss.block to see whether we searched all the + * ramblocks) to detect the completion of migration. Having NULL value + * of last_seen_block can conditionally cause below loop to run foreve= r. + */ + if (!rs->last_seen_block) { + rs->last_seen_block =3D QLIST_FIRST_RCU(&ram_list.blocks); + rs->last_page =3D 0; + } + pss.block =3D rs->last_seen_block; pss.page =3D rs->last_page; pss.complete_round =3D false; =20 - if (!pss.block) { - pss.block =3D QLIST_FIRST_RCU(&ram_list.blocks); - } - do { again =3D true; found =3D get_queued_page(rs, &pss); --=20 2.38.1