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Assert that the refcount value is not VPRC_BLOCKED in vm_page_drop().

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VPRC_BLOCKED is a refcount flag used to indicate that a thread is
tearing down mappings of a page.  When set, it causes attempts to wire a
page via a pmap lookup to fail.  It should never represent the last
reference to a page, so assert this.

Suggested by:	kib
Reviewed by:	alc, kib
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D21639
This commit is contained in:
Mark Johnston 2019-09-16 15:16:48 +00:00
parent 923da43e7c
commit 38547d5980
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=352411
1 changed files with 5 additions and 1 deletions
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6
sys/vm/vm_page.h
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@ -902,13 +902,17 @@ vm_page_in_laundry(vm_page_t m)
static inline u_int
vm_page_drop(vm_page_t m, u_int val)
{
u_int old;
/*
* Synchronize with vm_page_free_prep(): ensure that all updates to the
* page structure are visible before it is freed.
*/
atomic_thread_fence_rel();
return (atomic_fetchadd_int(&m->ref_count, -val));
old = atomic_fetchadd_int(&m->ref_count, -val);
KASSERT(old != VPRC_BLOCKED,
("vm_page_drop: page %p has an invalid refcount value", m));
return (old);
}
/*