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Date: Wed, 5 Sep 2018 15:00:08 -0700
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC PATCH] mm/hugetlb: make hugetlb_lock irq safe
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References: <20180905112341.21355-1-aneesh.kumar@linux.ibm.com>
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To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>, "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org

On Wed, 5 Sep 2018 14:35:11 -0700 Mike Kravetz <mike.kravetz@oracle.com> wrote:

> >                                            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.
> 
> I think we would add the warning/etc at free_huge_page.  The issue would
> only apply to hugetlb pages, not THP.
> 
> But, the more I think about it the more I think Aneesh's patch to do
> spin_lock/unlock_irqsave is the right way to go.  Currently, we only
> know of one place where a put_page of hugetlb pages is done from softirq
> context.  So, we could take the spin_lock/unlock_bh as Matthew suggested.
> When the powerpc iommu code was added, I doubt this was taken into account.
> I would be afraid of someone adding put_page from hardirq context.

Me too.  If we're going to do this, surely we should make hugepages
behave in the same fashion as PAGE_SIZE pages.