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?
