Commit d658bb36 authored by Xiongfeng Wang's avatar Xiongfeng Wang
Browse files

posix-cpu-timers: Implement timer_wait_running callback 

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7EQ8B



--------------------------------

For posix CPU timers, the .timer_wait_running() callback is missing,
which cause WARN_ON() in timer_wait_running().

Commit f7abf14f ("posix-cpu-timers: Implement the missing
timer_wait_running callback") solved the problem. But it introduce a
kabi broken which is hard to fix. The commit also describe a livelock
in preemptible kernel. To fix the livelock, we add cond_resched() in the
retry loop.

*** below is from origin commit merge tag
The reason is that for CONFIG_POSIX_CPU_TIMERS_TASK_WORK enabled
systems there is a livelock issue independent of RT.

CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y moves the expiry of POSIX CPU
timers out from hard interrupt context to task work, which is handled
before returning to user space or to a VM. The expiry mechanism moves
the expired timers to a stack local list head with sighand lock held.
Once sighand is dropped the task can be preempted and a task which
wants to delete a timer will spin-wait until the expiry task is
scheduled back in. In the worst case this will end up in a livelock
when the preempting task and the expiry task are pinned on the same
CPU.

Signed-off-by: default avatarXiongfeng Wang <wangxiongfeng2@huawei.com>
parent 411657bf

kernel/time/posix-cpu-timers.c

+16 −0
Original line number Diff line number Diff line
@@ -1446,6 +1446,9 @@ static int do_cpu_nanosleep(const clockid_t which_clock, int flags, 
			spin_lock_irq(&timer.it_lock);

			error = posix_cpu_timer_del(&timer);

			spin_unlock_irq(&timer.it_lock);

#ifdef CONFIG_POSIX_CPU_TIMERS_TASK_WORK

			cond_resched();

#endif

		}



		if ((it.it_value.tv_sec | it.it_value.tv_nsec) == 0) {
@@ -1546,6 +1549,18 @@ static int thread_cpu_timer_create(struct k_itimer *timer) 
	return posix_cpu_timer_create(timer);

}



static void posix_cpu_timer_wait_running(struct k_itimer *timr)

{

#ifdef CONFIG_POSIX_CPU_TIMERS_TASK_WORK

	rcu_read_unlock();

	cond_resched();

	rcu_read_lock();

#else

	cpu_relax();

#endif

}





const struct k_clock clock_posix_cpu = {

	.clock_getres		= posix_cpu_clock_getres,

	.clock_set		= posix_cpu_clock_set,
@@ -1556,6 +1571,7 @@ const struct k_clock clock_posix_cpu = { 
	.timer_del		= posix_cpu_timer_del,

	.timer_get		= posix_cpu_timer_get,

	.timer_rearm		= posix_cpu_timer_rearm,

	.timer_wait_running	= posix_cpu_timer_wait_running,

};



const struct k_clock clock_process = {