svn commit: r343719 - head/sys/vm
Mark Johnston
markj at FreeBSD.org
Sun Feb 3 18:39:00 UTC 2019
Author: markj
Date: Sun Feb 3 18:38:58 2019
New Revision: 343719
URL: https://svnweb.freebsd.org/changeset/base/343719
Log:
Fix a race in vm_page_dequeue_deferred().
To detect the case where the page is already marked for a deferred
dequeue, we must read the "queue" and "aflags" fields in a
precise order. Otherwise, a race with a concurrent
vm_page_dequeue_complete() could leave the page with PGA_DEQUEUE
set despite it already having been dequeued. Fix the problem by
using vm_page_queue() to check the queue state, which correctly
handles the race.
Reviewed by: kib
Tested by: pho
MFC after: 3 days
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D19039
Modified:
head/sys/vm/vm_page.c
Modified: head/sys/vm/vm_page.c
==============================================================================
--- head/sys/vm/vm_page.c Sun Feb 3 15:34:09 2019 (r343718)
+++ head/sys/vm/vm_page.c Sun Feb 3 18:38:58 2019 (r343719)
@@ -3279,18 +3279,13 @@ vm_page_dequeue_complete(vm_page_t m)
void
vm_page_dequeue_deferred(vm_page_t m)
{
- int queue;
+ uint8_t queue;
vm_page_assert_locked(m);
- queue = atomic_load_8(&m->queue);
- if (queue == PQ_NONE) {
- KASSERT((m->aflags & PGA_QUEUE_STATE_MASK) == 0,
- ("page %p has queue state", m));
+ if ((queue = vm_page_queue(m)) == PQ_NONE)
return;
- }
- if ((m->aflags & PGA_DEQUEUE) == 0)
- vm_page_aflag_set(m, PGA_DEQUEUE);
+ vm_page_aflag_set(m, PGA_DEQUEUE);
vm_pqbatch_submit_page(m, queue);
}
@@ -3386,7 +3381,7 @@ vm_page_requeue(vm_page_t m)
{
vm_page_assert_locked(m);
- KASSERT(m->queue != PQ_NONE,
+ KASSERT(vm_page_queue(m) != PQ_NONE,
("%s: page %p is not logically enqueued", __func__, m));
if ((m->aflags & PGA_REQUEUE) == 0)
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