From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sebastian Andrzej Siewior Subject: [RT PATCH 1/2] kernel/cpu_chill: use schedule_hrtimeout() Date: Fri, 16 Mar 2018 15:21:34 +0100 Message-ID: <20180316142135.9664-1-bigeasy@linutronix.de> Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, Steven Rostedt To: linux-rt-users@vger.kernel.org Return-path: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-rt-users.vger.kernel.org cpu_chill() uses __hrtimer_nanosleep() with a hack to get TASK_UNINTERRUPTIBLE state. It seems to work but it does not. The problem is that we may have a signal pending and receive a sporadic wake up _before_ the timer expires. At that point the code will look at ->restart_block and use it based on its value from the previous syscall resulting in a possible copy-to-user. Instead all this trouble, we could use schedule_hrtimeout() which is not an user-space interface and does not have this side effects. Cc: stable-rt@vger.kernel.org Signed-off-by: Sebastian Andrzej Siewior --- kernel/time/hrtimer.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index 6c77643eaf02..c0efc22ba635 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -1873,14 +1873,13 @@ COMPAT_SYSCALL_DEFINE2(nanosleep, struct compat_tim= espec __user *, rqtp, */ void cpu_chill(void) { - struct timespec64 tu =3D { - .tv_nsec =3D NSEC_PER_MSEC, - }; + ktime_t chill_time; unsigned int freeze_flag =3D current->flags & PF_NOFREEZE; =20 + chill_time =3D ktime_set(0, NSEC_PER_MSEC); + set_current_state(TASK_UNINTERRUPTIBLE); current->flags |=3D PF_NOFREEZE; - __hrtimer_nanosleep(&tu, HRTIMER_MODE_REL_HARD, CLOCK_MONOTONIC, - TASK_UNINTERRUPTIBLE); + schedule_hrtimeout(&chill_time, HRTIMER_MODE_REL_HARD); if (!freeze_flag) current->flags &=3D ~PF_NOFREEZE; } --=20 2.16.2