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bh=C43sXzuDPrCVxw3vYvZA3vkx4qjmhBG5GAMoIDyKDro=; b=YOJzGVdwAtnOnGSRfnOZiNZGFRu27wFDlPCh5oaf4VWxigpAb8x1653mhpj6MPTASGs8fc E0Yuih6P66O9ZCFUZLuSKOeMqGcJ3JIlg0SNyZPVjszZqY0ppl0T+3ztPT3WzzmtU9ghrq 1/XEAOwt732wVE4a4x56AIGbjf9nmqk= X-MC-Unique: clqyI-BYPgiqhT9ZfcFXAA-1 From: Juan Quintela To: qemu-devel@nongnu.org Cc: Stefan Hajnoczi , "Dr. David Alan Gilbert" , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , Fam Zheng , Juan Quintela , qemu-block@nongnu.org, David Hildenbrand , Peter Xu , Paolo Bonzini Subject: [PULL 3/8] migration: Fix possible infinite loop of ram save process Date: Mon, 21 Nov 2022 13:59:02 +0100 Message-Id: <20221121125907.62469-4-quintela@redhat.com> In-Reply-To: <20221121125907.62469-1-quintela@redhat.com> References: <20221121125907.62469-1-quintela@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 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=170.10.133.124; envelope-from=quintela@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-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+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1669035611914100003 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 dc1de9ddbc..1d42414ecc 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -2546,14 +2546,22 @@ 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