linux-kernel - Re: [PATCH] mm, numa: Fix bad pmd by atomically check for pmd_trans_huge when marking page tables prot

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Date:   Mon, 10 Apr 2017 18:20:56 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Zi Yan <zi.yan@...rutgers.edu>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm, numa: Fix bad pmd by atomically check for
 pmd_trans_huge when marking page tables prot_numa

On Mon, Apr 10, 2017 at 11:45:08AM -0500, Zi Yan wrote:
> > While this could be fixed with heavy locking, it's only necessary to
> > make a copy of the PMD on the stack during change_pmd_range and avoid
> > races. A new helper is created for this as the check if quite subtle and the
> > existing similar helpful is not suitable. This passed 154 hours of testing
> > (usually triggers between 20 minutes and 24 hours) without detecting bad
> > PMDs or corruption. A basic test of an autonuma-intensive workload showed
> > no significant change in behaviour.
> >
> > Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
> > Cc: stable@...r.kernel.org
> 
> Does this patch fix the same problem fixed by Kirill's patch here?
> https://lkml.org/lkml/2017/3/2/347
> 

I don't think so. The race I'm concerned with is due to locks not being
held and is in a different path.

-- 
Mel Gorman
SUSE Labs