linux-kernel - Re: blocking vs. non-blocking mmu notifiers

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Message-ID: <20220323170404.GK64706@ziepe.ca>
Date:   Wed, 23 Mar 2022 14:04:04 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Juergen Gross <jgross@...e.com>, linux-mm@...ck.org,
        lkml <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        Jerome Glisse <jglisse@...hat.com>
Subject: Re: blocking vs. non-blocking mmu notifiers

On Wed, Mar 23, 2022 at 05:49:43PM +0100, Michal Hocko wrote:
> > The bug here is that prior to commit a81461b0546c ("xen/gntdev: update
> > to new mmu_notifier semantic") wired the mn_invl_range_start() which
> > takes a mutex to invalidate_page, which is defined to run in an atomic
> > context.
> 
> Yeah, we have already identified that but quickly realized that the
> whole mmu notifier overhaul which this fix depends on would be no no for
> backporting to our older code base. So we are trying to find our way
> around that.

IMHO you don't need everything, just commit 369ea8242c0f ("mm/rmap:
update to new mmu_notifier semantic v2") which adds the missing
start/end outside the lock for the page callbacks.

Then you can take safely a8146 into gntdev.

Jason