[sync] PR-1727: add support for timer_shutdown() api · Pull Request !1744 · openEuler/kernel

### 1. Origin pull request:
https://gitee.com/openeuler/kernel/pulls/1727

### 2. Original pull request body:
PR sync from: Yu Liao <liaoyu15@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/N7DVTGONEIVDI2GITMMBE6T4J2YVA4WH/ 
timer_shutdown_sync() function is useful for final teardown of an
infrastructure where the timer is subject to a circular dependency
problem.

A common pattern for this is a timer and a workqueue where the timer can
schedule work and work can arm the timer. On shutdown the workqueue must
be destroyed and the timer must be prevented from rearming. Unless the
code has conditionals like 'if (mything->in_shutdown)' to prevent that
there is no way to get this correct with timer_delete_sync().

timer_shutdown_sync() is solving the problem. The correct ordering of
calls in this case is:

timer_shutdown_sync(&mything->timer);
 workqueue_destroy(&mything->workqueue);

After this 'mything' can be safely freed.

Steven Rostedt (Google) (3):
  ARM: spear: Do not use timer namespace for timer_shutdown() function
  clocksource/drivers/arm_arch_timer: Do not use timer namespace for
    timer_shutdown() function
  clocksource/drivers/sp804: Do not use timer namespace for
    timer_shutdown() function

Thomas Gleixner (10):
  timers: Get rid of del_singleshot_timer_sync()
  timers: Replace BUG_ON()s
  timers: Update kernel-doc for various functions
  timers: Use del_timer_sync() even on UP
  timers: Rename del_timer_sync() to timer_delete_sync()
  timers: Rename del_timer() to timer_delete()
  timers: Silently ignore timers with a NULL function
  timers: Add shutdown mechanism to the internal functions
  timers: Provide timer_shutdown[_sync]()

Yu Liao (2):
  sw64: Do not use timer namespace for timer_shutdown() function
  timers: Keep del_timer[_sync]() exported

-- 
2.25.1
 
https://gitee.com/openeuler/kernel/issues/I7R8WG

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