linux-kernel - Re: [RFC PATCH] mm/hugetlb: make hugetlb

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Message-ID: <20180905230737.GA14977@bombadil.infradead.org>
Date:   Wed, 5 Sep 2018 16:07:37 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] mm/hugetlb: make hugetlb_lock irq safe

On Wed, Sep 05, 2018 at 03:00:08PM -0700, Andrew Morton wrote:
> On Wed, 5 Sep 2018 14:35:11 -0700 Mike Kravetz <mike.kravetz@...cle.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.

But these aren't vanilla hugepages, they're specifically hugetlbfs pages.
I don't believe there's any problem with calling put_page() on a normally
allocated huge page or THP.