linux-kernel - Re: [PATCH] secure unlock_task

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Message-ID: <20131223142636.GA24504@redhat.com>
Date:	Mon, 23 Dec 2013 15:26:36 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	naveen yadav <yad.naveen@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Vaibhav Shinde <v.bhav.shinde@...il.com>,
	Ajeet Yadav <ajeet.yadav.77@...il.com>,
	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] secure unlock_task_sighand() call

On 12/23, naveen yadav wrote:
>
> Happy Christmas !!!

Thanks, the same to you ;)

> We are facing OOPS during core dump on kernel 3.8.x on ARM target.

Do you have any traces? Any additional info?

Can you try the fresh kernels?

Not that I can recall any change in this area which could help, but
perhaps this is arm specific...

> So we were doing core review and found this.

Do you mean that with this patch the kernel doesn't crash?

>  Also I think in zap_process() there is no need to send SIGKILL to
> ZOMBIE or DEAD process.

Yes, it would be very wrong to account a zombie, but:

> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -271,17 +271,19 @@ static int zap_process(struct task_struct
> *start, int exit_code)
>
> -               if (t != current && t->mm) {
> +               if (t->exit_state) {
> +                       nr++;
> +               } else if (t != current && t->mm) {

This change adds no harm, but it is misleading and unneeded. Please note
that t->mm != NULL && t->exit_state != 0 is not possible, exit_mm() is
called before exit_notify(). IOW, a zombie thread can't have ->mm.

Oleg.

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