Currently it's possible to hit an assertion in alloc_heap_pages():
Assertion 'first_dirty != INVALID_DIRTY_IDX || !(pg[i].count_info &
PGC_need_scrub)' failed at page_alloc.c:988
This can happen because a piece of logic to calculate first_dirty
during block merging in free_heap_pages() is missing for the following
scenario:
1. Current block's first_dirty equals to INVALID_DIRTY_IDX
2. Successor block is free but its first_dirty != INVALID_DIRTY_IDX
3. The successor is merged into current block
4. Current block's first_dirty still equals to INVALID_DIRTY_IDX
This will trigger the assertion during allocation of such block in
alloc_heap_pages() because there will be pages with PGC_need_scrub
bit set despite the claim of first_dirty that the block is scrubbed.
Add the missing piece of logic and slightly update the comment for
the predecessor case to better capture the code's intent.
Fixes 1a37f33ea613 ("mm: Place unscrubbed pages at the end of pagelist")
Signed-off-by: Sergey Dyasli <sergey.dya...@citrix.com>
---
CC: Andrew Cooper <andrew.coop...@citrix.com>
CC: George Dunlap <george.dun...@eu.citrix.com>
CC: Jan Beulich <jbeul...@suse.com>
CC: Julien Grall <julien.gr...@arm.com>
CC: Wei Liu <wei.l...@citrix.com>
CC: Boris Ostrovsky <boris.ostrov...@oracle.com>
---
xen/common/page_alloc.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 20ee1e4897..aa911f2dc5 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -1426,7 +1426,7 @@ static void free_heap_pages(
page_list_del(predecessor, &heap(node, zone, order));
- /* Keep predecessor's first_dirty if it is already set. */
+ /* Keep block's first_dirty if the predecessor doesn't have one */
if ( predecessor->u.free.first_dirty == INVALID_DIRTY_IDX &&
pg->u.free.first_dirty != INVALID_DIRTY_IDX )
predecessor->u.free.first_dirty = (1U << order) +
@@ -1447,6 +1447,12 @@ static void free_heap_pages(
check_and_stop_scrub(successor);
+ /* Keep successor's first_dirty if the block doesn't have one */
+ if ( pg->u.free.first_dirty == INVALID_DIRTY_IDX &&
+ successor->u.free.first_dirty != INVALID_DIRTY_IDX )
+ pg->u.free.first_dirty = (1U << order) +
+ successor->u.free.first_dirty;
+
page_list_del(successor, &heap(node, zone, order));
}
--
2.17.1
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