On 09/06/2018 01:28 AM, Andrew Morton wrote:
On Wed, 5 Sep 2018 06:48:48 -0700 Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
I didn't. The reason I looked at current patch is to enable the usage of
put_page() from irq context. We do allow that for non hugetlb pages. So was
not sure adding that additional restriction for hugetlb
is really needed. Further the conversion to irqsave/irqrestore was
straightforward.
straightforward, sure. but is it the right thing to do? do we want to
be able to put_page() a hugetlb page from hardirq context?
Calling put_page() against a huge page from hardirq seems like the
right thing to do - even if it's rare now, it will presumably become
more common as the hugepage virus spreads further across the kernel.
And the present asymmetry is quite a wart.
That being said, arch/powerpc/mm/mmu_context_iommu.c:mm_iommu_free() is
the only known site which does this (yes?) so perhaps we could put some
stopgap workaround into that site and add a runtime warning into the
put_page() code somewhere to detect puttage of huge pages from hardirq
and softirq contexts.
And attention will need to be paid to -stable backporting. How long
has mm_iommu_free() existed, and been doing this?
That is old code that goes back to v4.2 (
15b244a88e1b2895605be4300b40b575345bcf50)
-aneesh
