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mm: fix page table unmap for stack guard page properly

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We do in fact need to unmap the page table _before_ doing the whole
stack guard page logic, because if it is needed (mainly 32-bit x86 with
PAE and CONFIG_HIGHPTE, but other architectures may use it too) then it
will do a kmap_atomic/kunmap_atomic.

And those kmaps will create an atomic region that we cannot do
allocations in.  However, the whole stack expand code will need to do
anon_vma_prepare() and vma_lock_anon_vma() and they cannot do that in an
atomic region.

Now, a better model might actually be to do the anon_vma_prepare() when
_creating_ a VM_GROWSDOWN segment, and not have to worry about any of
this at page fault time.  But in the meantime, this is the
straightforward fix for the issue.

See https://bugzilla.kernel.org/show_bug.cgi?id=16588 for details.

Reported-by: Wylda <[email protected]>
Reported-by: Sedat Dilek <[email protected]>
Reported-by: Mike Pagano <[email protected]>
Reported-by: François Valenduc <[email protected]>
Tested-by: Ed Tomlinson <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Greg KH <[email protected]>
Cc: [email protected]
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Linus Torvalds 2010-08-14 11:44:56 -07:00
commit 11ac552477
1 changed files with 6 additions and 7 deletions
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15
mm/memory.c
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@ -2792,24 +2792,23 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
spinlock_t *ptl;
pte_t entry;
if (check_stack_guard_page(vma, address) < 0) {
pte_unmap(page_table);
return VM_FAULT_SIGBUS;
}
pte_unmap(page_table);
/* Check if we need to add a guard page to the stack */
if (check_stack_guard_page(vma, address) < 0)
return VM_FAULT_SIGBUS;
/* Use the zero-page for reads */
if (!(flags & FAULT_FLAG_WRITE)) {
entry = pte_mkspecial(pfn_pte(my_zero_pfn(address),
vma->vm_page_prot));
ptl = pte_lockptr(mm, pmd);
spin_lock(ptl);
page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
if (!pte_none(*page_table))
goto unlock;
goto setpte;
}
/* Allocate our own private page. */
pte_unmap(page_table);
if (unlikely(anon_vma_prepare(vma)))
goto oom;
page = alloc_zeroed_user_highpage_movable(vma, address);