From 6c5e9059692567740a4ee51530dffe51a4b9584d Mon Sep 17 00:00:00 2001 From: Douglas Anderson Date: Fri, 21 Oct 2016 08:58:50 -0700 Subject: [PATCH] timers: Fix usleep_range() in the context of wake_up_process() Users of usleep_range() expect that it will _never_ return in less time than the minimum passed parameter. However, nothing in the code ensures this, when the sleeping task is woken by wake_up_process() or any other mechanism which can wake a task from uninterruptible state. Neither usleep_range() nor schedule_hrtimeout_range*() have any protection against wakeups. schedule_hrtimeout_range*() is designed this way despite the fact that the API documentation does not mention it. msleep() already has code to handle this case since it will loop as long as there was still time left. usleep_range() has no such loop, add it. Presumably this problem was not detected before because usleep_range() is only used in a few places and the function is mostly used in contexts which are not exposed to wakeups of any form. An effort was made to look for users relying on the old behavior by looking for usleep_range() in the same file as wake_up_process(). No problems were found by this search, though it is conceivable that someone could have put the sleep and wakeup in two different files. An effort was made to ask several upstream maintainers if they were aware of people relying on wake_up_process() to wake up usleep_range(). No maintainers were aware of that but they were aware of many people relying on usleep_range() never returning before the minimum. Reported-by: Tao Huang Signed-off-by: Douglas Anderson Cc: heiko@sntech.de Cc: broonie@kernel.org Cc: briannorris@chromium.org Cc: Andreas Mohr Cc: linux-rockchip@lists.infradead.org Cc: tony.xie@rock-chips.com Cc: John Stultz Cc: djkurtz@chromium.org Cc: linux@roeck-us.net Cc: tskd08@gmail.com Link: http://lkml.kernel.org/r/1477065531-30342-1-git-send-email-dianders@chromium.org Signed-off-by: Thomas Gleixner --- kernel/time/timer.c | 21 +++++++++------------ 1 file changed, 9 insertions(+), 12 deletions(-) diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 2d47980a1bc4..12681c9a7683 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -1896,16 +1896,6 @@ unsigned long msleep_interruptible(unsigned int msecs) EXPORT_SYMBOL(msleep_interruptible); -static void __sched do_usleep_range(unsigned long min, unsigned long max) -{ - ktime_t kmin; - u64 delta; - - kmin = ktime_set(0, min * NSEC_PER_USEC); - delta = (u64)(max - min) * NSEC_PER_USEC; - schedule_hrtimeout_range(&kmin, delta, HRTIMER_MODE_REL); -} - /** * usleep_range - Sleep for an approximate time * @min: Minimum time in usecs to sleep @@ -1919,7 +1909,14 @@ static void __sched do_usleep_range(unsigned long min, unsigned long max) */ void __sched usleep_range(unsigned long min, unsigned long max) { - __set_current_state(TASK_UNINTERRUPTIBLE); - do_usleep_range(min, max); + ktime_t exp = ktime_add_us(ktime_get(), min); + u64 delta = (u64)(max - min) * NSEC_PER_USEC; + + for (;;) { + __set_current_state(TASK_UNINTERRUPTIBLE); + /* Do not return before the requested sleep time has elapsed */ + if (!schedule_hrtimeout_range(&exp, delta, HRTIMER_MODE_ABS)) + break; + } } EXPORT_SYMBOL(usleep_range); -- GitLab