Re: [EDT][PATCH] kernel/exit.c : Fix missing read_unlock

[Ingo Molnar]

* Maninder Singh <maninder1.s@xxxxxxxxxxx> wrote:

>  EP-F6AA0618C49C4AEDA73BFF1B39950BAB
> Hi,
> 
> From: Maninder Singh <maninder1.s@xxxxxxxxxxx>
> 
> 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@xxxxxxxxxxx>
> Signed-off-by: Vaneet Narang <v.narang@xxxxxxxxxxx>
> Reviewd-by: Akhilesh Kumar <akhilesh.k@xxxxxxxxxxx>
> ---
>  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@xxxxxxxxxx>
 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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