From 4934a5dd7c68f5ab15f17498db4fc20ed6db9578 Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Tue, 4 Oct 2022 14:24:26 -0400 Subject: [PATCH] migration: Fix possible infinite loop of ram save process 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; } + /* + * 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 forever. + */ + if (!rs->last_seen_block) { + rs->last_seen_block = QLIST_FIRST_RCU(&ram_list.blocks); + rs->last_page = 0; + } + pss.block = rs->last_seen_block; pss.page = rs->last_page; pss.complete_round = false; - if (!pss.block) { - pss.block = QLIST_FIRST_RCU(&ram_list.blocks); - } - do { again = true; found = get_queued_page(rs, &pss);