From: Rafael J. Wysocki <[email protected]> Theoretically, ktime_get_mono_fast_ns() may be executed after timekeeping has been suspended (or before it is resumed) which in turn may lead to undefined behavior, for example, when the clocksource read from timekeeping_get_ns() called by it is not accessible at that time.
Prevent that from happening by setting up a dummy readout base for the fast timekeeper during timekeeping_suspend() such that it will always return the same number of cycles. After the last timekeeping_update() in timekeeping_suspend() the clocksource is read and the result is stored as cycles_at_suspend. The readout base from the current timekeeper is copied onto the dummy and the ->read pointer of the dummy is set to a routine unconditionally returning cycles_at_suspend. Next, the dummy is passed to update_fast_timekeeper(). Then, ktime_get_mono_fast_ns() will work until the subsequent timekeeping_resume() and the proper readout base for the fast timekeeper will be restored by the timekeeping_update() called right after clearing timekeeping_suspended. Signed-off-by: Rafael J. Wysocki <[email protected]> --- kernel/time/timekeeping.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) Index: linux-pm/kernel/time/timekeeping.c =================================================================== --- linux-pm.orig/kernel/time/timekeeping.c +++ linux-pm/kernel/time/timekeeping.c @@ -1249,9 +1249,23 @@ static void timekeeping_resume(void) hrtimers_resume(); } +/* + * Dummy readout base and suspend-time cycles value for the fast timekeeper to + * work in a consistent way after timekeeping has been suspended if the core + * timekeeper clocksource is not suspend-nonstop. + */ +static struct tk_read_base tkr_dummy; +static cycle_t cycles_at_suspend; + +static cycle_t dummy_clock_read(struct clocksource *cs) +{ + return cycles_at_suspend; +} + static int timekeeping_suspend(void) { struct timekeeper *tk = &tk_core.timekeeper; + struct clocksource *clock = tk->tkr.clock; unsigned long flags; struct timespec64 delta, delta_delta; static struct timespec64 old_delta; @@ -1294,6 +1308,14 @@ static int timekeeping_suspend(void) } timekeeping_update(tk, TK_MIRROR); + + if (!(clock->flags & CLOCK_SOURCE_SUSPEND_NONSTOP)) { + memcpy(&tkr_dummy, &tk->tkr, sizeof(tkr_dummy)); + cycles_at_suspend = tk->tkr.read(clock); + tkr_dummy.read = dummy_clock_read; + update_fast_timekeeper(&tkr_dummy); + } + write_seqcount_end(&tk_core.seq); raw_spin_unlock_irqrestore(&timekeeper_lock, flags); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
