Commit-ID: 61bb4bcb79c7afcd0bf0d20aef4704977172fd60 Gitweb: https://git.kernel.org/tip/61bb4bcb79c7afcd0bf0d20aef4704977172fd60 Author: Anna-Maria Gleixner <[email protected]> AuthorDate: Thu, 21 Dec 2017 11:41:48 +0100 Committer: Ingo Molnar <[email protected]> CommitDate: Tue, 16 Jan 2018 02:53:58 +0100
hrtimer: Unify hrtimer removal handling When the first hrtimer on the current CPU is removed, hrtimer_force_reprogram() is invoked but only when CONFIG_HIGH_RES_TIMERS=y and hrtimer_cpu_base.hres_active is set. hrtimer_force_reprogram() updates hrtimer_cpu_base.expires_next and reprograms the clock event device. When CONFIG_HIGH_RES_TIMERS=y and hrtimer_cpu_base.hres_active is set, a pointless hrtimer interrupt can be prevented. hrtimer_check_target() makes the 'can remote enqueue' decision. As soon as hrtimer_check_target() is unconditionally available and hrtimer_cpu_base.expires_next is updated by hrtimer_reprogram(), hrtimer_force_reprogram() needs to be available unconditionally as well to prevent the following scenario with CONFIG_HIGH_RES_TIMERS=n: - the first hrtimer on this CPU is removed and hrtimer_force_reprogram() is not executed - CPU goes idle (next timer is calculated and hrtimers are taken into account) - a hrtimer is enqueued remote on the idle CPU: hrtimer_check_target() compares expiry value and hrtimer_cpu_base.expires_next. The expiry value is after expires_next, so the hrtimer is enqueued. This timer will fire late, if it expires before the effective first hrtimer on this CPU and the comparison was with an outdated expires_next value. To prevent this scenario, make hrtimer_force_reprogram() unconditional except the effective reprogramming part, which gets eliminated by the compiler in the CONFIG_HIGH_RES_TIMERS=n case. Signed-off-by: Anna-Maria Gleixner <[email protected]> Cc: Christoph Hellwig <[email protected]> Cc: John Stultz <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: [email protected] Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> --- kernel/time/hrtimer.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index 2b3222e..e6a78ae 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -521,9 +521,6 @@ hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal) { ktime_t expires_next; - if (!__hrtimer_hres_active(cpu_base)) - return; - expires_next = __hrtimer_get_next_event(cpu_base); if (skip_equal && expires_next == cpu_base->expires_next) @@ -532,6 +529,9 @@ hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal) cpu_base->expires_next = expires_next; /* + * If hres is not active, hardware does not have to be + * reprogrammed yet. + * * If a hang was detected in the last timer interrupt then we * leave the hang delay active in the hardware. We want the * system to make progress. That also prevents the following @@ -545,7 +545,7 @@ hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal) * set. So we'd effectivly block all timers until the T2 event * fires. */ - if (cpu_base->hang_detected) + if (!__hrtimer_hres_active(cpu_base) || cpu_base->hang_detected) return; tick_program_event(cpu_base->expires_next, 1); @@ -844,7 +844,6 @@ static void __remove_hrtimer(struct hrtimer *timer, if (!timerqueue_del(&base->active, &timer->node)) cpu_base->active_bases &= ~(1 << base->index); -#ifdef CONFIG_HIGH_RES_TIMERS /* * Note: If reprogram is false we do not update * cpu_base->next_timer. This happens when we remove the first @@ -855,7 +854,6 @@ static void __remove_hrtimer(struct hrtimer *timer, */ if (reprogram && timer == cpu_base->next_timer) hrtimer_force_reprogram(cpu_base, 1); -#endif } /*
