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: Xiongfeng Wang <wangxiongfeng2@huawei.com>