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Relax an assertion in vm_pqbatch_process_page().

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While executing vm_pqbatch_process_page(m), m->queue may change to
PQ_NONE if the page daemon is concurrently freeing the page.  In this
case m's queue state flags must be clear, so vm_pqbatch_process_page()
will be a no-op, but the race could cause spurious assertion failures.
Correct the assertion which assumed that m->queue's value does not
change while the page queue lock is held.

Reviewed by:	alc, kib
Reported and tested by:	pho
Approved by:	re (gjb)
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D17027
This commit is contained in:
markj 2018-09-08 21:49:43 +00:00
parent e5ee207835
commit 933d701a36
1 changed files with 16 additions and 9 deletions
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25
sys/vm/vm_page.c
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@ -3107,28 +3107,35 @@ static inline void
vm_pqbatch_process_page(struct vm_pagequeue *pq, vm_page_t m)
{
struct vm_domain *vmd;
uint8_t aflags;
uint8_t qflags;
CRITICAL_ASSERT(curthread);
vm_pagequeue_assert_locked(pq);
KASSERT(pq == vm_page_pagequeue(m),
("page %p doesn't belong to %p", m, pq));
aflags = m->aflags;
if ((aflags & PGA_DEQUEUE) != 0) {
if (__predict_true((aflags & PGA_ENQUEUED) != 0)) {
/*
* The page daemon is allowed to set m->queue = PQ_NONE without
* the page queue lock held. In this case it is about to free the page,
* which must not have any queue state.
*/
qflags = atomic_load_8(&m->aflags) & PGA_QUEUE_STATE_MASK;
KASSERT(pq == vm_page_pagequeue(m) || qflags == 0,
("page %p doesn't belong to queue %p but has queue state %#x",
m, pq, qflags));
if ((qflags & PGA_DEQUEUE) != 0) {
if (__predict_true((qflags & PGA_ENQUEUED) != 0)) {
TAILQ_REMOVE(&pq->pq_pl, m, plinks.q);
vm_pagequeue_cnt_dec(pq);
}
vm_page_dequeue_complete(m);
} else if ((aflags & (PGA_REQUEUE | PGA_REQUEUE_HEAD)) != 0) {
if ((aflags & PGA_ENQUEUED) != 0)
} else if ((qflags & (PGA_REQUEUE | PGA_REQUEUE_HEAD)) != 0) {
if ((qflags & PGA_ENQUEUED) != 0)
TAILQ_REMOVE(&pq->pq_pl, m, plinks.q);
else {
vm_pagequeue_cnt_inc(pq);
vm_page_aflag_set(m, PGA_ENQUEUED);
}
if ((aflags & PGA_REQUEUE_HEAD) != 0) {
if ((qflags & PGA_REQUEUE_HEAD) != 0) {
KASSERT(m->queue == PQ_INACTIVE,
("head enqueue not supported for page %p", m));
vmd = vm_pagequeue_domain(m);