Messages in this thread | | | Date | Thu, 7 Mar 2013 18:53:05 +0100 | From | Oleg Nesterov <> | Subject | [PATCH 0/1] thinkpad-acpi: kill hotkey_thread_mutex |
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On 03/06, Henrique de Moraes Holschuh wrote: > > On Wed, 06 Mar 2013, Oleg Nesterov wrote: > > > > static void hotkey_poll_stop_sync(void) > > { > > if (tpacpi_hotkey_task) { > > kthread_stop(tpacpi_hotkey_task); > > tpacpi_hotkey_task = NULL; > > mutex_lock(&hotkey_thread_mutex); > > /* at this point, the thread did exit */ > > mutex_unlock(&hotkey_thread_mutex); > > } > > } > > > > And I simply do not understand the comment. This thread has already exited > > when kthread_stop() returns (OK, it can be running do_exit() paths but this > > doesn't matter). So this mutex_lock() buys nothing afaics. > > It was added due to an oops, waaaaay back then. If it is not needed > anymore, and there is zero chance of the kthread still being active when > hotkey_poll_stop_sync() ends, hotkey_thread_mutex can be simply removed.
Well, there could be another bug. Say, hotkey_poll_stop_sync() can block on hotkey_thread_mutex if another thread was started. But at first glance this can't happen (hotkey_mutex), and even _if_ it can this needs another fix.
> Looks like it, if the current semanthics of ktread_stop() are syncronous.
IIRC, it always was... But at least currently it is certainly syncronous. kthread_stop(t) does wait_for_completion(t->vfork_done), complete(vfork_done) can't happen unless this task calls do_exit().
Hmm. I just noticed that the recent changes in kthread_stop() are not correct... But this is offtopic and doesn't affect thinkpad_acpi.c, I'll write another email later.
So, what do you think about (UNTESTED) 1/1 ?
Oleg.
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