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vm: Fix some bugs in the page busying code

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In vm_page_busy_acquire(), load the object pointer using
atomic_load_ptr() as we do elsewhere.  Per the comment, the object
identity must be consistent across sleeps.

In vm_page_grab_sleep(), pass the correct pindex to
_vm_page_busy_sleep().  The pindex is used to re-check the page's
identity before going to sleep.  In particular, vm_page_grab_sleep() is
used in unlocked grab, so the object lock is not necessarily held when
verifying the page's identity, and the pindex may change if the page is
moved, or freed and re-allocated.  I believe this can result in spurious
VM_PAGER_FAILs from vm_page_grab_valid_unlocked() or early termination
of vm_page_grab_pages_unlocked().

In vm_page_grab_pages(), pass the correct pindex to
vm_page_grab_sleep().  Otherwise I believe vm_page_grab_pages() will
effectively spin when attempting to busy a busy page after the first
index in the range.

Reviewed by:	alc, kib
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D27607
This commit is contained in:
Mark Johnston 2020-12-27 16:50:54 -05:00
parent d2f1c44bc9
commit 81846def34
1 changed files with 4 additions and 4 deletions
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8
sys/vm/vm_page.c
View file

@ -882,7 +882,7 @@ vm_page_busy_acquire(vm_page_t m, int allocflags)
* It is assumed that a reference to the object is already
* held by the callers.
*/
obj = m->object;
obj = atomic_load_ptr(&m->object);
for (;;) {
if (vm_page_tryacquire(m, allocflags))
return (true);
@ -4386,8 +4386,8 @@ vm_page_grab_sleep(vm_object_t object, vm_page_t m, vm_pindex_t pindex,
if (locked && (allocflags & VM_ALLOC_NOCREAT) == 0)
vm_page_reference(m);
if (_vm_page_busy_sleep(object, m, m->pindex, wmesg, allocflags,
locked) && locked)
if (_vm_page_busy_sleep(object, m, pindex, wmesg, allocflags, locked) &&
locked)
VM_OBJECT_WLOCK(object);
if ((allocflags & VM_ALLOC_WAITFAIL) != 0)
return (false);
@ -4780,7 +4780,7 @@ retrylookup:
for (; i < count; i++) {
if (m != NULL) {
if (!vm_page_tryacquire(m, allocflags)) {
if (vm_page_grab_sleep(object, m, pindex,
if (vm_page_grab_sleep(object, m, pindex + i,
"grbmaw", allocflags, true))
goto retrylookup;
break;