Re: [PATCH 2/2] posix_timer: clean up properly if anything failsafter *_timer_create

From: Andrew Vagin
Date: Sat May 15 2010 - 10:15:30 EST


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@xxxxxxxxxx> 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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