On Tue, Dec 11, 2018 at 01:26:59PM +0300, Kirill Tkhai wrote: > ksm thread unconditionally sleeps in ksm_scan_thread() > after each iteration: > > schedule_timeout_interruptible( > msecs_to_jiffies(ksm_thread_sleep_millisecs)) > > The timeout is configured in /sys/kernel/mm/ksm/sleep_millisecs. > > In case of user writes a big value by a mistake, and the thread > enters into schedule_timeout_interruptible(), it's not possible > to cancel the sleep by writing a new smaler value; the thread > is just sleeping till timeout expires. > > The patch fixes the problem by waking the thread each time > after the value is updated. > > This also may be useful for debug purposes; and also for userspace > daemons, which change sleep_millisecs value in dependence of > system load. > > Signed-off-by: Kirill Tkhai <[email protected]> > > v2: Use wait_event_interruptible_timeout() instead of unconditional > schedule_timeout(). ... > @@ -2844,7 +2849,10 @@ static ssize_t sleep_millisecs_store(struct kobject > *kobj, > if (err || msecs > UINT_MAX) > return -EINVAL; > > + mutex_lock(&ksm_thread_mutex); > ksm_thread_sleep_millisecs = msecs; > + mutex_unlock(&ksm_thread_mutex); > + wake_up_interruptible(&ksm_iter_wait);
Btw, just thought -- if we start using this mutex here don't we open a window for force attack on the thread self execution, iow if there gonna be a million of writers do we have a guarantee thread ksm_scan_thread will grab the mutex earlier than writers (or somewhere inbetween)?
