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

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Date:	Thu, 21 May 2015 12:32:10 +0200
From:	Frans Klaver <fransklaver@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Maninder Singh <maninder1.s@...sung.com>,
	Andrew Morton <akpm@...ux-foundation.org>, oleg@...hat.com,
	Michal Hocko <mhocko@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>, ionut.m.alexa@...il.com,
	Peter Hurley <peter@...leysoftware.com>,
	"linux-kernel@...r.kernel.org" <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

On Thu, May 21, 2015 at 8:03 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * 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 <snip>

Still it looks like it is a legitimate change. I don't see where the
unlock would be done otherwise.

I do wonder if this would look nicer if the whole locked part would be
pulled out into a separate (inline) function. That would render the
repeated read_unlock()s unnecessary and possibly also prevent a
goto/label mess if that were to be attempted in-line.

Frans
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