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 <wylda@volny.cz> Reported-by:
Sedat Dilek <sedat.dilek@gmail.com> Reported-by:
Mike Pagano <mpagano@gentoo.org> Reported-by:
François Valenduc <francois.valenduc@tvcablenet.be> Tested-by:
Ed Tomlinson <edt@aei.ca> Cc: Pekka Enberg <penberg@kernel.org> Cc: Greg KH <gregkh@suse.de> Cc: stable@kernel.org Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org>
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