linux-kernel - Re: [PATCH 2/2] posix_timer: clean up properly if anything fails after *_timer

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Message-ID: <4BEEACED.8030004@gmail.com>
Date:	Sat, 15 May 2010 18:17:17 +0400
From:	Andrew Vagin <avagin@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Stanislaw Gruszka <sgruszka@...hat.com>,
	Andrey Vagin <avagin@...nvz.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [PATCH 2/2] posix_timer: clean up properly if anything fails
 after *_timer_create

On 05/14/2010 10:48 PM, Oleg Nesterov wrote:
> On 05/14, Stanislaw Gruszka wrote:
>    
>> On Fri, 14 May 2010 18:03:57 +0200
>> Oleg Nesterov<oleg@...hat.com>  wrote:
>>
>>      
>>> On 05/14, Andrey Vagin wrote:
>>>        
>>>> @@ -613,6 +613,8 @@ SYSCALL_DEFINE3(timer_create, const clockid_t, which_clock,
>>>>   	 * and may cease to exist at any time.  Don't use or modify
>>>>   	 * new_timer after the unlock call.
>>>>   	 */
>>>> +out_cleanup:
>>>> +	CLOCK_DISPATCH(new_timer->it_clock, timer_cleanup, (new_timer));
>>>>          
>>> But at first glance you are right, posix_cpu_timer_create() does
>>> get_task_struct(it.cpu.task).
>>>        
>> If I understand problem correctly, seems to be fine to move
>> CLOCK_DISPATCH(which_clock, timer_create, (new_timer));
>> after all possible EFAULT errors and solve leak without creating
>> new timer_cleanup() callback.
>>      
> I thought about this too, we are doing copy_to_user(created_timer_id)
> "in advance" anyway. Probably we can move all this code block
>
> 	new_timer->it_id = (timer_t) new_timer_id;
> 	new_timer->it_clock = which_clock;
> 	new_timer->it_overrun = -1;
> 	error = CLOCK_DISPATCH(which_clock, timer_create, (new_timer));
> 	if (error)
> 		goto out;
>
> down, right before we take ->siglock.
>    
You are right. I will send a new patch sooner. Thanks for your comments.
> But I don't understand the change in posix_cpu_timer_del() from 1/2.
>    
timer_cleanup doesn't do the disarm timer. In case fail in timer_create 
it's enough to call timer_cleanup. This changes are not necessary in new 
version.
>
> Otoh, currently "The next step is hard to back out if there is an error"
> comment is not right, release_posix_timer() does put_pid(). We can
> move copy_to_user(created_timer_id) down after "if (timer_event_spec)"
> block too. (but before CLOCK_DISPATCH(), of course).
>
> Andrey, what do you think?
>    
I've look at code again and think that you are right. At first I created 
patches for 2.6.18 kernel, more complex code in this place and the 
comment "the next step is ..." induced me to make callback timer_cleanup.
> Oleg.
>
>    

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