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

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Message-ID: <20150521181616.GA18981@redhat.com>
Date:	Thu, 21 May 2015 20:16:16 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Maninder Singh <maninder1.s@...sung.com>
Cc:	akpm@...ux-foundation.org, mhocko@...e.cz, peterz@...radead.org,
	mingo@...nel.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>
Subject: Re: [EDT][PATCH] kernel/exit.c : Fix missing read_unlock

On 05/21, Maninder Singh 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.

Confused...

wait_consider_task() should drop tasklist_lock if it returns non-zero?


> --- 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;
> +		}

Well, the patch is obviously wrong. Because, again, tasklist_lock was
already unlocked if (say) wait_task_zombie() reaps a child.

If you think there is a case which forgets to unlock, please tell us
more.

Oleg.

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