Change Details

r332974 was somewhat sloppy in that I did not properly audit callers of `vm_page_active()` and so on. Code like the following is racy after that revision: ``` vm_page_assert_locked(m); if (vm_page_active(m)) vm_page_reference(m); else vm_page_requeue(m); ``` in particular, `PGA_DEQUEUE` might be set on m, in which case `m->queue` may change to PQ_NONE after the `vm_page_active()` call but before the `vm_page_requeue()` call. (Note that once `m->queue` has transitioned to `PQ_NONE`, the page lock prevents further updates to the `queue` field.) Add a function, `vm_page_queue()`, which reads `m->queue` with the appropriate synchronization. It requires the page lock. Use this function where appropriate.

r332974 was somewhat sloppy in that I did not properly audit callers of `vm_page_active()` and so on. Code like the following is racy after that revision: ``` vm_page_assert_locked(m); if (m->queue == PQ_ACTIVE) vm_page_reference(m); else vm_page_requeue(m); ``` in particular, `PGA_DEQUEUE` might be set on m, in which case `m->queue` may change to PQ_NONE after the `vm_page_active()` call but before the `vm_page_requeue()` call. (Note that once `m->queue` has transitioned to `PQ_NONE`, the page lock prevents further updates to the `queue` field.) Add a function, `vm_page_queue()`, which reads `m->queue` with the appropriate synchronization. It requires the page lock. Use this function where appropriate.

r332974 was somewhat sloppy in that I did not properly audit callers of `vm_page_active()` and so on. Code like the following is racy after that revision: ``` vm_page_assert_locked(m); if (vm_page_active(m)m->queue == PQ_ACTIVE) vm_page_reference(m); else vm_page_requeue(m); ``` in particular, `PGA_DEQUEUE` might be set on m, in which case `m->queue` may change to PQ_NONE after the `vm_page_active()` call but before the `vm_page_requeue()` call. (Note that once `m->queue` has transitioned to `PQ_NONE`, the page lock prevents further updates to the `queue` field.) Add a function, `vm_page_queue()`, which reads `m->queue` with the appropriate synchronization. It requires the page lock. Use this function where appropriate.