linux-kernel - Re: [EDT][PATCH] kernel/exit.c : Fix missing read

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Date:	Thu, 21 May 2015 08:03:48 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Maninder Singh <maninder1.s@...sung.com>
Cc:	akpm@...ux-foundation.org, oleg@...hat.com, mhocko@...e.cz,
	peterz@...radead.org, riel@...hat.com, ionut.m.alexa@...il.com,
	peter@...leysoftware.com, linux-kernel@...r.kernel.org,
	"v.narang@...sung.com" <v.narang@...sung.com>,
	AKHILESH KUMAR <akhilesh.k@...sung.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [EDT][PATCH] kernel/exit.c : Fix missing read_unlock


* Maninder Singh <maninder1.s@...sung.com> wrote:

>  EP-F6AA0618C49C4AEDA73BFF1B39950BAB
> Hi,
> 
> From: Maninder Singh <maninder1.s@...sung.com>
> 
> Subject: [PATCH 1/1] kernel/exit.c : Fix missing task_unlock
> 
> This patch adds missing read_unlock if do_wait_thread or ptrace_do_wait 
> returns non zero.
> 
> Signed-off-by: Maninder Singh <maninder1.s@...sung.com>
> Signed-off-by: Vaneet Narang <v.narang@...sung.com>
> Reviewd-by: Akhilesh Kumar <akhilesh.k@...sung.com>
> ---
>  kernel/exit.c |    8 ++++++--
>  1 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 22fcc05..31a061f 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -1486,12 +1486,16 @@ repeat:
>  	tsk = current;
>  	do {
>  		retval = do_wait_thread(wo, tsk);
> -		if (retval)
> +		if (retval) {
> +			read_unlock(&tasklist_lock);
>  			goto end;
> +		}
>  
>  		retval = ptrace_do_wait(wo, tsk);
> -		if (retval)
> +		if (retval) {
> +			read_unlock(&tasklist_lock);
>  			goto end;
> +		}
>  
>  		if (wo->wo_flags & __WNOTHREAD)
>  			break;

That's surprising and the changelog is lacking.

So the last time that code was touched upstream was 7 years ago:

 commit 64a16caf5e3417ee32f670debcb5857b02a9e08e
 Author: Oleg Nesterov <oleg@...hat.com>
 Date:   Wed Jun 17 16:27:40 2009 -0700

    do_wait: simplify retval/tsk_result/notask_error mess

please explain whether what you fix is:

  1) an ancient bug that somehow nobody ever triggered (plus analysis 
     of why it wasn't triggered)

  2) a new bug introduced by commit XYZ (plus analysis)

  3) something else

Thanks,

	Ingo
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