[PATCH v2] timers: Fix usleep_range() in the context of wake_up_process()
djkurtz at chromium.org
Tue Oct 18 06:44:16 PDT 2016
On Tue, Oct 11, 2016 at 5:04 AM, Douglas Anderson <dianders at chromium.org> wrote:
> Users of usleep_range() expect that it will _never_ return in less time
> than the minimum passed parameter. However, nothing in any of the code
> ensures this. Specifically:
> usleep_range() => do_usleep_range() => schedule_hrtimeout_range() =>
> schedule_hrtimeout_range_clock() just ends up calling schedule() with an
> appropriate timeout set using the hrtimer. If someone else happens to
> wake up our task then we'll happily return from usleep_range() early.
I think this change works, and fixes a real issue, however, I don't
think you are fixing this at the right layer.
The comment for schedule_hrtimeout_range says:
* schedule_hrtimeout_range - sleep until timeout
* @expires: timeout value (ktime_t)
* @delta: slack in expires timeout (ktime_t)
* @mode: timer mode, HRTIMER_MODE_ABS or HRTIMER_MODE_REL
* Make the current task sleep until the given expiry time has
* elapsed. The routine will return immediately unless
* the current task state has been set (see set_current_state()).
* The @delta argument gives the kernel the freedom to schedule the
* actual wakeup to a time that is both power and performance friendly.
* The kernel give the normal best effort behavior for "@expires+ at delta",
* but may decide to fire the timer earlier, but no earlier than @expires.
* You can set the task state as follows -
* %TASK_UNINTERRUPTIBLE - at least @timeout time is guaranteed to
* pass before the routine returns.
* %TASK_INTERRUPTIBLE - the routine may return early if a signal is
* delivered to the current task.
* The current task state is guaranteed to be TASK_RUNNING when this
* routine returns.
* Returns 0 when the timer has expired otherwise -EINTR
The behavior as specified for this function "at least @timeout time is
guaranteed to pass before the routine returns" already guarantees the
behavior you are adding to do_usleep_range() whenever the current task
state is (pre-)set to TASK_UNINTERRUPTIBLE.
Thus, I think the loop around 'schedule()' should be moved to
This would also fix direct callers of schedule_hrtimeout_range() that
use TASK_UNINTERRUPTIBLE, although, I could only find one:
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