Re: mpol_to_str revisited.

From: KOSAKI Motohiro
Date: Tue Oct 16 2012 - 19:39:42 EST

On Tue, Oct 16, 2012 at 2:10 AM, David Rientjes <rientjes@xxxxxxxxxx> 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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