Date: Wed, 8 Jul 2009 10:07:31 -0500 (CDT) From: Mark Tinguely <tinguely@casselton.net> To: mih@semihalf.com, tinguely@casselton.net Cc: stas@FreeBSD.org, freebsd-arm@FreeBSD.org Subject: Re: pmap problem in FreeBSD current Message-ID: <200907081507.n68F7Vsu070524@casselton.net> In-Reply-To: <4A54A6B2.1020400@semihalf.com>
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> Hello Mark,
> Thank you for looking again on r194459.
>
> I've tried to compile kernel using your patch with
> changes regarding PG_WRITABLE and arm_unmap_nocache(),
> but it didn't help.
>
> My problems are rather related to memory corruption, which
> I've observed in uma_core (pointers had bad values and
> count of free items in slab had negative value).
>
> I am still concerned about LOR, which has appeared in
> svn commit r194459 (I wrote about it in my first mail).
> Could you take a look at this LOR?
>
> Thanks for your help.
>
> Best regards,
> Michał Hajduk
I don't think this is a corruption issue but an allocation of a l2_bucket
issue. The kernel map is locked to do the kenter. A new bucket is needed,
UMA is called and the new page is kenter into the map. In pmap_enter_pv()
before we allocate a pv_entry, we turn off the kmap lock. I am not sure if
the kmap lock should be turned off in the pmap_alloc_l2_bucket(), or the
caller, but here is a quick manually made kmap lock disable patch:
I still think the last "vm_page_flag_clear(pg, PG_WRITEABLE);" needs
to be removed from pmap_nuke_pv(). All dangling kenters need to be
kremoved ...
------------------------
/*
* Returns a pointer to the L2 bucket associated with the specified pmap
* and VA.
*
* If no L2 bucket exists, perform the necessary allocations to put an L2
* bucket/page table in place.
*
* Note that if a new L2 bucket/page was allocated, the caller *must*
* increment the bucket occupancy counter appropriately *before*
* releasing the pmap's lock to ensure no other thread or cpu deallocates
* the bucket/page in the meantime.
*/
static struct l2_bucket *
pmap_alloc_l2_bucket(pmap_t pm, vm_offset_t va)
{
struct l2_dtable *l2;
struct l2_bucket *l2b;
u_short l1idx;
+ int km = 0;
l1idx = L1_IDX(va);
PMAP_ASSERT_LOCKED(pm);
+ if ((pm != pmap_kernel()) && PMAP_OWNED(pmap_kernel()) {
+ km = 1;
+ PMAP_UNLOCK(pmap_kernel());
+ }
mtx_assert(&vm_page_queue_mtx, MA_OWNED);
if ((l2 = pm->pm_l2[L2_IDX(l1idx)]) == NULL) {
/*
* No mapping at this address, as there is
* no entry in the L1 table.
* Need to allocate a new l2_dtable.
*/
again_l2table:
PMAP_UNLOCK(pm);
vm_page_unlock_queues();
if ((l2 = pmap_alloc_l2_dtable()) == NULL) {
vm_page_lock_queues();
PMAP_LOCK(pm);
+ if (km)
+ PMAP_LOCK(pmap_kernel());
return (NULL);
}
vm_page_lock_queues();
PMAP_LOCK(pm);
if (pm->pm_l2[L2_IDX(l1idx)] != NULL) {
PMAP_UNLOCK(pm);
vm_page_unlock_queues();
uma_zfree(l2table_zone, l2);
vm_page_lock_queues();
PMAP_LOCK(pm);
l2 = pm->pm_l2[L2_IDX(l1idx)];
if (l2 == NULL)
goto again_l2table;
/*
* Someone already allocated the l2_dtable while
* we were doing the same.
*/
} else {
bzero(l2, sizeof(*l2));
/*
* Link it into the parent pmap
*/
pm->pm_l2[L2_IDX(l1idx)] = l2;
}
}
l2b = &l2->l2_bucket[L2_BUCKET(l1idx)];
/*
* Fetch pointer to the L2 page table associated with the address.
*/
if (l2b->l2b_kva == NULL) {
pt_entry_t *ptep;
/*
* No L2 page table has been allocated. Chances are, this
* is because we just allocated the l2_dtable, above.
*/
again_ptep:
PMAP_UNLOCK(pm);
vm_page_unlock_queues();
ptep = (void*)uma_zalloc(l2zone, M_NOWAIT|M_USE_RESERVE);
vm_page_lock_queues();
PMAP_LOCK(pm);
if (l2b->l2b_kva != 0) {
/* We lost the race. */
PMAP_UNLOCK(pm);
vm_page_unlock_queues();
uma_zfree(l2zone, ptep);
vm_page_lock_queues();
PMAP_LOCK(pm);
if (l2b->l2b_kva == 0)
goto again_ptep;
return (l2b);
}
l2b->l2b_phys = vtophys(ptep);
if (ptep == NULL) {
/*
* Oops, no more L2 page tables available at this
* time. We may need to deallocate the l2_dtable
* if we allocated a new one above.
*/
if (l2->l2_occupancy == 0) {
pm->pm_l2[L2_IDX(l1idx)] = NULL;
pmap_free_l2_dtable(l2);
}
+ if (km)
+ PMAP_LOCK(pmap_kernel());
return (NULL);
}
l2->l2_occupancy++;
l2b->l2b_kva = ptep;
l2b->l2b_l1idx = l1idx;
}
+ if (km)
+ PMAP_LOCK(pmap_kernel());
return (l2b);
}
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