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

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Date:	Fri, 22 May 2015 03:36:51 +0000 (GMT)
From:	Maninder Singh <maninder1.s@...sung.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mhocko@...e.cz" <mhocko@...e.cz>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"riel@...hat.com" <riel@...hat.com>,
	"ionut.m.alexa@...il.com" <ionut.m.alexa@...il.com>,
	"peter@...leysoftware.com" <peter@...leysoftware.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [EDT][PATCH] kernel/exit.c : Fix missing read_unlock

 EP-F6AA0618C49C4AEDA73BFF1B39950BAB

Hi Oleg,

>> 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.

Yes, agree, My wrong
>If you think there is a case which forgets to unlock, please tell us
>more.
I have checked It is getting unlocked in wait_task_zombie Sorry for unnecessary disturbance. 

>Oleg.
Thanks