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When downgrading exclusively busied page to shared-busy state, wakeup

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waiters.  Otherwise, owners of the shared-busy state are left blocked
and might get into a deadlock.

Note that the vm_page_busy_downgrade() function is not used in the
tree right now.

Reported and tested by:	pho (previous version)
Reviewed by:	alc, markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D8195
This commit is contained in:
Konstantin Belousov 2016-10-11 18:09:37 +00:00
parent 199511bcdd
commit 267ed8e2f7
1 changed files with 12 additions and 1 deletions
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13
sys/vm/vm_page.c
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@ -655,15 +655,26 @@ void
vm_page_busy_downgrade(vm_page_t m)
{
u_int x;
bool locked;
vm_page_assert_xbusied(m);
locked = mtx_owned(vm_page_lockptr(m));
for (;;) {
x = m->busy_lock;
x &= VPB_BIT_WAITERS;
if (x != 0 && !locked)
vm_page_lock(m);
if (atomic_cmpset_rel_int(&m->busy_lock,
VPB_SINGLE_EXCLUSIVER | x, VPB_SHARERS_WORD(1) | x))
VPB_SINGLE_EXCLUSIVER | x, VPB_SHARERS_WORD(1)))
break;
if (x != 0 && !locked)
vm_page_unlock(m);
}
if (x != 0) {
wakeup(m);
if (!locked)
vm_page_unlock(m);
}
}