linux-kernel - Re: [RFC v7 PATCH 4/4] mm: unmap special vmas with regular do

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Message-ID: <20180810115937.GB1644@dhcp22.suse.cz>
Date:   Fri, 10 Aug 2018 13:59:37 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Yang Shi <yang.shi@...ux.alibaba.com>, willy@...radead.org,
        ldufour@...ux.vnet.ibm.com, kirill@...temov.name,
        akpm@...ux-foundation.org, peterz@...radead.org, mingo@...hat.com,
        acme@...nel.org, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC v7 PATCH 4/4] mm: unmap special vmas with regular
 do_munmap()

On Fri 10-08-18 11:51:54, Vlastimil Babka wrote:
> On 08/10/2018 01:36 AM, Yang Shi wrote:
> > Unmapping vmas, which have VM_HUGETLB | VM_PFNMAP flag set or
> > have uprobes set, need get done with write mmap_sem held since
> > they may update vm_flags.
> > 
> > So, it might be not safe enough to deal with these kind of special
> > mappings with read mmap_sem. Deal with such mappings with regular
> > do_munmap() call.
> > 
> > Michal suggested to make this as a separate patch for safer and more
> > bisectable sake.
> 
> Hm I believe Michal meant the opposite "evolution" though. Patch 2/4
> should be done in a way that special mappings keep using the regular
> path, and this patch would convert them to the new path. Possibly even
> each special case separately.

yes, that is what I meant. Each of the special case should have its own
patch and changelog explaining why it is safe.
-- 
Michal Hocko
SUSE Labs