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

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Date:   Thu, 24 Mar 2022 13:42:56 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
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 23-03-22 14:04:04, Jason Gunthorpe wrote:
> 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.

Thanks Jason!

-- 
Michal Hocko
SUSE Labs