Hi Doug, 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 schedule_hrtimeout_range() itself. This would also fix direct callers of schedule_hrtimeout_range() that use TASK_UNINTERRUPTIBLE, although, I could only find one: pt3_fetch_thread() -Dan
