The patch titled
clocksource: sanity check sysfs clocksource changes
has been added to the -mm tree. Its filename is
clocksource-sanity-check-sysfs-clocksource-changes.patch
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Subject: clocksource: sanity check sysfs clocksource changes
From: john stultz <johnstul@xxxxxxxxxx>
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.
This patch tries to correct this by filtering non HRT clocksources from
available_clocksources and not accepting non HRT clocksources with HRT is
is enabled.
This has been lightly tested, and seems to work, but there may be some
drawbacks.
One issue I realized was that when TSCs disqualified, they are marked as
not CLOCK_SOURCE_VALID_FOR_HRES. This means on boxes with unsycned TSCs,
the only available clocksource may be the slower acpi_pm and the user will
not be able to override it with the TSC as is currently possible. (even
if that seems ill-advised).
So Thomas, what do you think? Should we just use
CLOCK_SOURCE_IS_CONTINUOUS flag or is CLOCK_SOURCE_VALID_FOR_HRES really
what we want?
Signed-off-by: John Stultz <johnstul@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
(akpm: still an rfc)
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/hrtimer.h | 2 +-
kernel/hrtimer.c | 4 ++--
kernel/time/clocksource.c | 17 ++++++++++++++++-
3 files changed, 19 insertions(+), 4 deletions(-)
diff -puN include/linux/hrtimer.h~clocksource-sanity-check-sysfs-clocksource-changes include/linux/hrtimer.h
--- a/include/linux/hrtimer.h~clocksource-sanity-check-sysfs-clocksource-changes
+++ a/include/linux/hrtimer.h
@@ -305,7 +305,7 @@ static inline int hrtimer_is_hres_active
extern ktime_t ktime_get(void);
extern ktime_t ktime_get_real(void);
-
+extern int hrtimer_hres_active(void);
DECLARE_PER_CPU(struct tick_device, tick_cpu_device);
diff -puN kernel/hrtimer.c~clocksource-sanity-check-sysfs-clocksource-changes kernel/hrtimer.c
--- a/kernel/hrtimer.c~clocksource-sanity-check-sysfs-clocksource-changes
+++ a/kernel/hrtimer.c
@@ -476,7 +476,7 @@ static inline int hrtimer_is_hres_enable
/*
* Is the high resolution mode active ?
*/
-static inline int hrtimer_hres_active(void)
+int hrtimer_hres_active(void)
{
return __get_cpu_var(hrtimer_bases).hres_active;
}
@@ -691,7 +691,7 @@ static int hrtimer_switch_to_hres(void)
#else
-static inline int hrtimer_hres_active(void) { return 0; }
+int hrtimer_hres_active(void) { return 0; }
static inline int hrtimer_is_hres_enabled(void) { return 0; }
static inline int hrtimer_switch_to_hres(void) { return 0; }
static inline void hrtimer_force_reprogram(struct hrtimer_cpu_base *base) { }
diff -puN kernel/time/clocksource.c~clocksource-sanity-check-sysfs-clocksource-changes kernel/time/clocksource.c
--- a/kernel/time/clocksource.c~clocksource-sanity-check-sysfs-clocksource-changes
+++ a/kernel/time/clocksource.c
@@ -30,6 +30,7 @@
#include <linux/module.h>
#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
#include <linux/tick.h>
+#include <linux/hrtimer.h>
/* XXX - Would like a better way for initializing curr_clocksource */
extern struct clocksource clocksource_jiffies;
@@ -436,6 +437,17 @@ static ssize_t sysfs_override_clocksourc
}
}
+ /* 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;
@@ -464,7 +476,10 @@ sysfs_show_available_clocksources(struct
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);
}
_
Patches currently in -mm which might be from johnstul@xxxxxxxxxx are
clocksource-pass-clocksource-to-read-callback.patch
clocksource-add-enable-and-disable-callbacks.patch
clocksource-sanity-check-sysfs-clocksource-changes.patch
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