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Date: Fri, 21 Oct 2016 08:58:51 -0700 From: Douglas Anderson <dianders@...omium.org> To: Thomas Gleixner <tglx@...utronix.de>, John Stultz <john.stultz@...aro.org> Cc: Andreas Mohr <andi@...as.de>, briannorris@...omium.org, huangtao@...k-chips.com, tony.xie@...k-chips.com, linux-rockchip@...ts.infradead.org, linux@...ck-us.net, heiko@...ech.de, broonie@...nel.org, djkurtz@...omium.org, tskd08@...il.com, Douglas Anderson <dianders@...omium.org>, linux-kernel@...r.kernel.org Subject: [PATCH v5 2/2] timers: Fix documentation for schedule_timeout() and similar The documentatoin for schedule_timeout(), schedule_hrtimeout(), and schedule_hrtimeout_range() all claimed that the routines couldn't possibly return early if the task state was TASK_UNINTERRUPTIBLE. This was simply not true since anyone calling wake_up_process() would cause those routines to exit early. As some evidence that the documentation was broken (not the code): - If we changed the code to match the documentation, msleep() would be identical to schedule_timeout_uninterruptible() and msleep_interruptible() would be identical to schedule_timeout_interruptible(). That doesn't seem likely to have been the intention. - The schedule() function sleeps until a task is woken up. Logically, one would expect that the schedule_timeout() function would sleep until a task is woken up or a timeout occurrs. As part of the above observation, it can be seen that schedule_hrtimeout() and schedule_hrtimeout_range() might return -EINTR even if the task state was TASK_UNINTERRUPTIBLE. This isn't terrible behavior so we'll document it and keep it as-is. After all, trying to match schedule_timeout() and return the time left would incure a bunch of extra calculation cost that isn't needed in all cases. Suggested-by: Daniel Kurtz <djkurtz@...omium.org> Signed-off-by: Douglas Anderson <dianders@...omium.org> --- Changes in v5: None Changes in v4: - Fixed stray double quotes. - Updated wording as per Thomas Gleixner. Changes in v3: - Documentation fix new for v3. kernel/time/hrtimer.c | 20 ++++++++++++++------ kernel/time/timer.c | 11 +++++++---- 2 files changed, 21 insertions(+), 10 deletions(-) diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index bb5ec425dfe0..08be5c99d26b 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -1742,15 +1742,19 @@ schedule_hrtimeout_range_clock(ktime_t *expires, u64 delta, * You can set the task state as follows - * * %TASK_UNINTERRUPTIBLE - at least @timeout time is guaranteed to - * pass before the routine returns. + * pass before the routine returns unless the current task is explicitly + * woken up, (e.g. by wake_up_process()). * * %TASK_INTERRUPTIBLE - the routine may return early if a signal is - * delivered to the current task. + * delivered to the current task or the current task is explicitly woken + * up. * * The current task state is guaranteed to be TASK_RUNNING when this * routine returns. * - * Returns 0 when the timer has expired otherwise -EINTR + * Returns 0 when the timer has expired. If the task was woken before the + * timer expired by a signal (only possible in state TASK_INTERRUPTIBLE) or + * by an explicit wakeup, it returns -EINTR. */ int __sched schedule_hrtimeout_range(ktime_t *expires, u64 delta, const enum hrtimer_mode mode) @@ -1772,15 +1776,19 @@ EXPORT_SYMBOL_GPL(schedule_hrtimeout_range); * You can set the task state as follows - * * %TASK_UNINTERRUPTIBLE - at least @timeout time is guaranteed to - * pass before the routine returns. + * pass before the routine returns unless the current task is explicitly + * woken up, (e.g. by wake_up_process()). * * %TASK_INTERRUPTIBLE - the routine may return early if a signal is - * delivered to the current task. + * delivered to the current task or the current task is explicitly woken + * up. * * The current task state is guaranteed to be TASK_RUNNING when this * routine returns. * - * Returns 0 when the timer has expired otherwise -EINTR + * Returns 0 when the timer has expired. If the task was woken before the + * timer expired by a signal (only possible in state TASK_INTERRUPTIBLE) or + * by an explicit wakeup, it returns -EINTR. */ int __sched schedule_hrtimeout(ktime_t *expires, const enum hrtimer_mode mode) diff --git a/kernel/time/timer.c b/kernel/time/timer.c index ab65e7bcc2c2..330214a19beb 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -1691,11 +1691,12 @@ static void process_timeout(unsigned long __data) * You can set the task state as follows - * * %TASK_UNINTERRUPTIBLE - at least @timeout jiffies are guaranteed to - * pass before the routine returns. The routine will return 0 + * pass before the routine returns unless the current task is explicitly + * woken up, (e.g. by wake_up_process())". * * %TASK_INTERRUPTIBLE - the routine may return early if a signal is - * delivered to the current task. In this case the remaining time - * in jiffies will be returned, or 0 if the timer expired in time + * delivered to the current task or the current task is explicitly woken + * up. * * The current task state is guaranteed to be TASK_RUNNING when this * routine returns. @@ -1704,7 +1705,9 @@ static void process_timeout(unsigned long __data) * the CPU away without a bound on the timeout. In this case the return * value will be %MAX_SCHEDULE_TIMEOUT. * - * In all cases the return value is guaranteed to be non-negative. + * Returns 0 when the timer has expired otherwise the remaining time in + * jiffies will be returned. In all cases the return value is guaranteed + * to be non-negative. */ signed long __sched schedule_timeout(signed long timeout) { -- 2.8.0.rc3.226.g39d4020
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