mm: fix page table unmap for stack guard page properly

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]>

0 files changed, 0 insertions, 0 deletions