From 3f68535adad8dd89499505a65fb25d0e02d118cc Mon Sep 17 00:00:00 2001 From: john stultz Date: Wed, 21 Jan 2009 22:53:22 -0700 Subject: clocksource: sanity check sysfs clocksource changes Thomas, Andrew and Ingo pointed out that we don't have any safety checks in the clocksource sysfs entries to make sure sysadmins don't try to change the clocksource to a non high-res timer capable clocksource (such as jiffies) when high-res timers (HRT) is enabled. Doing so will likely hang a system. Correct this by filtering non HRT clocksources from available_clocksources and not accepting non HRT clocksources with HRT enabled. Signed-off-by: John Stultz Signed-off-by: Andrew Morton Signed-off-by: Thomas Gleixner --- kernel/time/clocksource.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) (limited to 'kernel/time') diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 80189f6f1c5a..18b9f5da4ee9 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -30,6 +30,7 @@ #include #include /* for spin_unlock_irq() using preempt_count() m68k */ #include +#include void timecounter_init(struct timecounter *tc, const struct cyclecounter *cc, @@ -509,6 +510,18 @@ static ssize_t sysfs_override_clocksource(struct sys_device *dev, } } + /* + * Check to make sure we don't switch to a non-HRT usable + * clocksource if HRT is enabled and running + */ + if (hrtimer_hres_active() && + !(ovr->flags & CLOCK_SOURCE_VALID_FOR_HRES)) { + printk(KERN_WARNING "%s clocksource is not HRT compatible. " + "Cannot switch while in HRT mode\n", ovr->name); + ovr = NULL; + override_name[0] = 0; + } + /* Reselect, when the override name has changed */ if (ovr != clocksource_override) { clocksource_override = ovr; @@ -537,7 +550,10 @@ sysfs_show_available_clocksources(struct sys_device *dev, spin_lock_irq(&clocksource_lock); list_for_each_entry(src, &clocksource_list, list) { - count += snprintf(buf + count, + /* Don't show non-HRES clocksource if HRES is enabled */ + if (!hrtimer_hres_active() || + (src->flags & CLOCK_SOURCE_VALID_FOR_HRES)) + count += snprintf(buf + count, max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "%s ", src->name); } -- cgit v1.2.3 From cd6d95d8449b7c9f415f26041e9ae173d387b6bd Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 12 Jun 2009 11:29:27 +0200 Subject: clocksource: prevent selection of low resolution clocksourse also for nohz=on commit 3f68535adad (clocksource: sanity check sysfs clocksource changes) prevents selection of non high resolution capable clocksources when high resolution mode is active, but did not take into account that the same rules apply for highres=off nohz=on. Check the tick device mode instead of hrtimer_hres_active() to verify whether the system needs to be protected from a switch to jiffies or other non highres capable clock sources. Reported-by: Luming Yu Signed-off-by: Thomas Gleixner --- kernel/time/clocksource.c | 18 ++++++++++-------- kernel/time/tick-oneshot.c | 17 +++++++++++++++++ 2 files changed, 27 insertions(+), 8 deletions(-) (limited to 'kernel/time') diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 18b9f5da4ee9..592bf584d1d2 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -30,7 +30,6 @@ #include #include /* for spin_unlock_irq() using preempt_count() m68k */ #include -#include void timecounter_init(struct timecounter *tc, const struct cyclecounter *cc, @@ -511,13 +510,13 @@ static ssize_t sysfs_override_clocksource(struct sys_device *dev, } /* - * Check to make sure we don't switch to a non-HRT usable - * clocksource if HRT is enabled and running + * Check to make sure we don't switch to a non-highres capable + * clocksource if the tick code is in oneshot mode (highres or nohz) */ - if (hrtimer_hres_active() && + if (tick_oneshot_mode_active() && !(ovr->flags & CLOCK_SOURCE_VALID_FOR_HRES)) { printk(KERN_WARNING "%s clocksource is not HRT compatible. " - "Cannot switch while in HRT mode\n", ovr->name); + "Cannot switch while in HRT/NOHZ mode\n", ovr->name); ovr = NULL; override_name[0] = 0; } @@ -550,9 +549,12 @@ sysfs_show_available_clocksources(struct sys_device *dev, spin_lock_irq(&clocksource_lock); list_for_each_entry(src, &clocksource_list, list) { - /* Don't show non-HRES clocksource if HRES is enabled */ - if (!hrtimer_hres_active() || - (src->flags & CLOCK_SOURCE_VALID_FOR_HRES)) + /* + * Don't show non-HRES clocksource if the tick code is + * in one shot mode (highres=on or nohz=on) + */ + if (!tick_oneshot_mode_active() || + (src->flags & CLOCK_SOURCE_VALID_FOR_HRES)) count += snprintf(buf + count, max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "%s ", src->name); diff --git a/kernel/time/tick-oneshot.c b/kernel/time/tick-oneshot.c index 2e8de678e767..a96c0e2b89cf 100644 --- a/kernel/time/tick-oneshot.c +++ b/kernel/time/tick-oneshot.c @@ -128,6 +128,23 @@ int tick_switch_to_oneshot(void (*handler)(struct clock_event_device *)) return 0; } +/** + * tick_check_oneshot_mode - check whether the system is in oneshot mode + * + * returns 1 when either nohz or highres are enabled. otherwise 0. + */ +int tick_oneshot_mode_active(void) +{ + unsigned long flags; + int ret; + + local_irq_save(flags); + ret = __get_cpu_var(tick_cpu_device).mode == TICKDEV_MODE_ONESHOT; + local_irq_restore(flags); + + return ret; +} + #ifdef CONFIG_HIGH_RES_TIMERS /** * tick_init_highres - switch to high resolution mode -- cgit v1.2.3