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Revert "vm: use atomic fetchadd in vm_page_sunbusy"

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This reverts commit f6ffed44a8.

fetchadd will fail the waiters flag, which can cause other
code to wait when it should not with nothing clear it

Revert until I sort this out.

Reported by:	markj
This commit is contained in:
Mateusz Guzik 2022-08-17 16:24:14 +00:00
parent e674ddec0b
commit 1b89d40fbf
1 changed files with 20 additions and 6 deletions
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26
sys/vm/vm_page.c
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@ -973,13 +973,27 @@ vm_page_sunbusy(vm_page_t m)
{
u_int x;
atomic_thread_fence_rel();
x = atomic_fetchadd_int(&m->busy_lock, -VPB_ONE_SHARER);
KASSERT(x != VPB_FREED, ("page %p is freed", m));
KASSERT(x != VPB_UNBUSIED && (x & VPB_BIT_SHARED) != 0,
("page %p not sbusied", m));
if (x == (VPB_SHARERS_WORD(1) | VPB_BIT_WAITERS))
vm_page_assert_sbusied(m);
x = vm_page_busy_fetch(m);
for (;;) {
KASSERT(x != VPB_FREED,
("vm_page_sunbusy: Unlocking freed page."));
if (VPB_SHARERS(x) > 1) {
if (atomic_fcmpset_int(&m->busy_lock, &x,
x - VPB_ONE_SHARER))
break;
continue;
}
KASSERT((x & ~VPB_BIT_WAITERS) == VPB_SHARERS_WORD(1),
("vm_page_sunbusy: invalid lock state"));
if (!atomic_fcmpset_rel_int(&m->busy_lock, &x, VPB_UNBUSIED))
continue;
if ((x & VPB_BIT_WAITERS) == 0)
break;
wakeup(m);
break;
}
}
/*