linux-kernel - Re: [PATCH] skip increamenting nr for TASK

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Message-ID: <CA+55aFwBwrindu1AJU4S7XgYyxpuBUyq=wrwdDVn2EJUuChVDg@mail.gmail.com>
Date:	Sat, 21 Dec 2013 09:47:17 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Vaibhav Shinde <v.bhav.shinde@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Ajeet Yadav <ajeet.yadav.77@...il.com>
Cc:	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] skip increamenting nr for TASK_UNINTERRUPTIBLE

Again, adding Oleg to the cc. And I don't think this is correct, since
SIGKILL can actually kill uninterruptible processes too
(TASK_WAKEKILL) so the basic premise of the patch is incorrect. And
again, we do have that whole issue with exit_mm() serialization.

                   Linus

On Sat, Dec 21, 2013 at 4:18 AM, Vaibhav Shinde <v.bhav.shinde@...il.com> wrote:
> Dear All,
>
> We found below issue in coredump for uninterruptible task -
>
> From 1c46f0327d98ad593d8913f9f1dad352f8f44304 Mon Sep 17 00:00:00 2001
> From: Ajeet Yadav <ajeet.yadav.77@...il.com>
> Date: Sat, 21 Dec 2013 17:06:05 +0530
> Subject: [PATCH] skip increamenting nr for TASK_UNINTERRUPTIBLE
>
> In coredump case, where thread_1 faults while thread_2 is in
> TASK_UNINTERRUPTIBLE state, it cannot handle the SIGKILL.
> Thus the process hangs on event.
> The coredump routine freezes until the thread state is
> uninterruptible.
>
> Solution: Continue for coredump, without waiting for uninterruptible
>  thread, as it will get killed as soon as it returns from
>  uninterruptible state.
>  Therefore do not increament thread count for threads with
>  TASK_UNINTERRUPTIBLE.
>
> Signed-off-by: Ajeet Yadav <ajeet.yadav.77@...il.com>
> Signed-off-by: Vaibhav Shinde <v.bhav.shinde@...il.com>
> ---
>  fs/coredump.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/fs/coredump.c b/fs/coredump.c
> index 447b02c..54b0664 100644
> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -281,7 +281,8 @@ static int zap_process(struct task_struct *start,
> int exit_code)
>   if (t != current && t->mm) {
>   sigaddset(&t->pending.signal, SIGKILL);
>   signal_wake_up(t, 1);
> - nr++;
> + if(!(t->state & TASK_UNINTERRUPTIBLE))
> + nr++;
>   }
>   } while_each_thread(start, t);
>
> --
> 1.7.9.5
--
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