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From: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Date: Tue, 16 Oct 2012 19:39:29 -0400
Message-ID: <CAHGf_=pemT6rcbu=dBVSJE7GuGWwVFP+Wn-mwkcsZ_gBGfaOsg@mail.gmail.com>
Subject: Re: mpol_to_str revisited.
To: David Rientjes <rientjes@google.com>
Cc: Dave Jones <davej@redhat.com>, Linux Kernel <linux-kernel@vger.kernel.org>,
        bhutchings@solarflare.com, linux-mm@kvack.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>
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On Tue, Oct 16, 2012 at 2:10 AM, David Rientjes <rientjes@google.com> wrote:
> On Tue, 16 Oct 2012, KOSAKI Motohiro wrote:
>
>> >> I don't think 80de7c3138ee9fd86a98696fd2cf7ad89b995d0a is right fix.
>> >
>> > It's certainly not a complete fix, but I think it's a much better result
>> > of the race, i.e. we don't panic anymore, we simply fail the read()
>> > instead.
>>
>> Even though 80de7c3138ee9fd86a98696fd2cf7ad89b995d0a itself is simple. It bring
>> to caller complex. That's not good and have no worth.
>>
>
> Before: the kernel panics, all workloads cease.
> After: the file shows garbage, all workloads continue.
>
> This is better, in my opinion, but at best it's only a judgment call and
> has no effect on anything.

Kernel panics help to find our serious mistake.


> I agree it would be better to respect the return value of mpol_to_str()
> since there are other possible error conditions other than a freed
> mempolicy, but let's not consider reverting 80de7c3138.  It is obviously
> not a full solution to the problem, though, and we need to serialize with
> task_lock().

Sorry no. I will have to revert it. mempolicy have already a lot of
meaningless complex and bring us a lot of problems. I haven't
seen any reason adding more.


> Dave, are you interested in coming up with a patch?
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