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[PULL 3/8] migration: Fix possible infinite loop of ram save process
From: |
Juan Quintela |
Subject: |
[PULL 3/8] migration: Fix possible infinite loop of ram save process |
Date: |
Mon, 21 Nov 2022 13:59:02 +0100 |
From: Peter Xu <peterx@redhat.com>
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 <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
---
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);
--
2.38.1
- [PULL 0/8] Next patches, Juan Quintela, 2022/11/21
- [PULL 1/8] migration/channel-block: fix return value for qio_channel_block_{readv, writev}, Juan Quintela, 2022/11/21
- [PULL 2/8] migration/multifd/zero-copy: Create helper function for flushing, Juan Quintela, 2022/11/21
- [PULL 3/8] migration: Fix possible infinite loop of ram save process,
Juan Quintela <=
- [PULL 4/8] migration: Fix race on qemu_file_shutdown(), Juan Quintela, 2022/11/21
- [PULL 5/8] migration: Disallow postcopy preempt to be used with compress, Juan Quintela, 2022/11/21
- [PULL 8/8] migration: Block migration comment or code is wrong, Juan Quintela, 2022/11/21
- [PULL 7/8] migration: Disable multifd explicitly with compression, Juan Quintela, 2022/11/21
- [PULL 6/8] migration: Use non-atomic ops for clear log bitmap, Juan Quintela, 2022/11/21
- Re: [PULL 0/8] Next patches, Stefan Hajnoczi, 2022/11/21