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 f7abf14f0001 ("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: Xiongfeng Wang wangxiongfeng2@huawei.com --- kernel/time/posix-cpu-timers.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c index c97bc3e3b210..578d0ebedb67 100644 --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -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 = {