[tip:timers/urgent] clocksource: Revert "Remove kthread"
Commit-ID: e2c631ba75a7e727e8db0a9d30a06bfd434adb3a
Gitweb: https://git.kernel.org/tip/e2c631ba75a7e727e8db0a9d30a06bfd434adb3a
Author: Peter Zijlstra
AuthorDate: Wed, 5 Sep 2018 10:41:58 +0200
Committer: Thomas Gleixner
CommitDate: Thu, 6 Sep 2018 23:38:35 +0200
clocksource: Revert "Remove kthread"
I turns out that the silly spawn kthread from worker was actually needed.
clocksource_watchdog_kthread() cannot be called directly from
clocksource_watchdog_work(), because clocksource_select() calls
timekeeping_notify() which uses stop_machine(). One cannot use
stop_machine() from a workqueue() due lock inversions wrt CPU hotplug.
Revert the patch but add a comment that explain why we jump through such
apparently silly hoops.
Fixes: 7197e77abcb6 ("clocksource: Remove kthread")
Reported-by: Siegfried Metz
Signed-off-by: Peter Zijlstra (Intel)
Signed-off-by: Thomas Gleixner
Tested-by: Niklas Cassel
Tested-by: Kevin Shanahan
Tested-by: viktor_jaegerskuep...@freenet.de
Tested-by: Siegfried Metz
Cc: rafael.j.wyso...@intel.com
Cc: len.br...@intel.com
Cc: diego.vi...@gmail.com
Cc: rui.zh...@intel.com
Cc: bjorn.anders...@linaro.org
Link:
https://lkml.kernel.org/r/20180905084158.gr24...@hirez.programming.kicks-ass.net
---
kernel/time/clocksource.c | 40 ++--
1 file changed, 30 insertions(+), 10 deletions(-)
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index f74fb00d8064..0e6e97a01942 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -133,19 +133,40 @@ static void inline clocksource_watchdog_unlock(unsigned
long *flags)
spin_unlock_irqrestore(_lock, *flags);
}
+static int clocksource_watchdog_kthread(void *data);
+static void __clocksource_change_rating(struct clocksource *cs, int rating);
+
/*
* Interval: 0.5sec Threshold: 0.0625s
*/
#define WATCHDOG_INTERVAL (HZ >> 1)
#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
+static void clocksource_watchdog_work(struct work_struct *work)
+{
+ /*
+* We cannot directly run clocksource_watchdog_kthread() here, because
+* clocksource_select() calls timekeeping_notify() which uses
+* stop_machine(). One cannot use stop_machine() from a workqueue() due
+* lock inversions wrt CPU hotplug.
+*
+* Also, we only ever run this work once or twice during the lifetime
+* of the kernel, so there is no point in creating a more permanent
+* kthread for this.
+*
+* If kthread_run fails the next watchdog scan over the
+* watchdog_list will find the unstable clock again.
+*/
+ kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
+}
+
static void __clocksource_unstable(struct clocksource *cs)
{
cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
cs->flags |= CLOCK_SOURCE_UNSTABLE;
/*
-* If the clocksource is registered clocksource_watchdog_work() will
+* If the clocksource is registered clocksource_watchdog_kthread() will
* re-rate and re-select.
*/
if (list_empty(>list)) {
@@ -156,7 +177,7 @@ static void __clocksource_unstable(struct clocksource *cs)
if (cs->mark_unstable)
cs->mark_unstable(cs);
- /* kick clocksource_watchdog_work() */
+ /* kick clocksource_watchdog_kthread() */
if (finished_booting)
schedule_work(_work);
}
@@ -166,7 +187,7 @@ static void __clocksource_unstable(struct clocksource *cs)
* @cs:clocksource to be marked unstable
*
* This function is called by the x86 TSC code to mark clocksources as
unstable;
- * it defers demotion and re-selection to a work.
+ * it defers demotion and re-selection to a kthread.
*/
void clocksource_mark_unstable(struct clocksource *cs)
{
@@ -391,9 +412,7 @@ static void clocksource_dequeue_watchdog(struct clocksource
*cs)
}
}
-static void __clocksource_change_rating(struct clocksource *cs, int rating);
-
-static int __clocksource_watchdog_work(void)
+static int __clocksource_watchdog_kthread(void)
{
struct clocksource *cs, *tmp;
unsigned long flags;
@@ -418,12 +437,13 @@ static int __clocksource_watchdog_work(void)
return select;
}
-static void clocksource_watchdog_work(struct work_struct *work)
+static int clocksource_watchdog_kthread(void *data)
{
mutex_lock(_mutex);
- if (__clocksource_watchdog_work())
+ if (__clocksource_watchdog_kthread())
clocksource_select();
mutex_unlock(_mutex);
+ return 0;
}
static bool clocksource_is_watchdog(struct clocksource *cs)
@@ -442,7 +462,7 @@ static void clocksource_enqueue_watchdog(struct clocksource
*cs)
static void clocksource_select_watchdog(bool fallback) { }
static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
static inline void clocksource_resume_watchdog(void) { }
-static
[tip:timers/urgent] clocksource: Revert "Remove kthread"
Commit-ID: e2c631ba75a7e727e8db0a9d30a06bfd434adb3a
Gitweb: https://git.kernel.org/tip/e2c631ba75a7e727e8db0a9d30a06bfd434adb3a
Author: Peter Zijlstra
AuthorDate: Wed, 5 Sep 2018 10:41:58 +0200
Committer: Thomas Gleixner
CommitDate: Thu, 6 Sep 2018 23:38:35 +0200
clocksource: Revert "Remove kthread"
I turns out that the silly spawn kthread from worker was actually needed.
clocksource_watchdog_kthread() cannot be called directly from
clocksource_watchdog_work(), because clocksource_select() calls
timekeeping_notify() which uses stop_machine(). One cannot use
stop_machine() from a workqueue() due lock inversions wrt CPU hotplug.
Revert the patch but add a comment that explain why we jump through such
apparently silly hoops.
Fixes: 7197e77abcb6 ("clocksource: Remove kthread")
Reported-by: Siegfried Metz
Signed-off-by: Peter Zijlstra (Intel)
Signed-off-by: Thomas Gleixner
Tested-by: Niklas Cassel
Tested-by: Kevin Shanahan
Tested-by: viktor_jaegerskuep...@freenet.de
Tested-by: Siegfried Metz
Cc: rafael.j.wyso...@intel.com
Cc: len.br...@intel.com
Cc: diego.vi...@gmail.com
Cc: rui.zh...@intel.com
Cc: bjorn.anders...@linaro.org
Link:
https://lkml.kernel.org/r/20180905084158.gr24...@hirez.programming.kicks-ass.net
---
kernel/time/clocksource.c | 40 ++--
1 file changed, 30 insertions(+), 10 deletions(-)
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index f74fb00d8064..0e6e97a01942 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -133,19 +133,40 @@ static void inline clocksource_watchdog_unlock(unsigned
long *flags)
spin_unlock_irqrestore(_lock, *flags);
}
+static int clocksource_watchdog_kthread(void *data);
+static void __clocksource_change_rating(struct clocksource *cs, int rating);
+
/*
* Interval: 0.5sec Threshold: 0.0625s
*/
#define WATCHDOG_INTERVAL (HZ >> 1)
#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
+static void clocksource_watchdog_work(struct work_struct *work)
+{
+ /*
+* We cannot directly run clocksource_watchdog_kthread() here, because
+* clocksource_select() calls timekeeping_notify() which uses
+* stop_machine(). One cannot use stop_machine() from a workqueue() due
+* lock inversions wrt CPU hotplug.
+*
+* Also, we only ever run this work once or twice during the lifetime
+* of the kernel, so there is no point in creating a more permanent
+* kthread for this.
+*
+* If kthread_run fails the next watchdog scan over the
+* watchdog_list will find the unstable clock again.
+*/
+ kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
+}
+
static void __clocksource_unstable(struct clocksource *cs)
{
cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
cs->flags |= CLOCK_SOURCE_UNSTABLE;
/*
-* If the clocksource is registered clocksource_watchdog_work() will
+* If the clocksource is registered clocksource_watchdog_kthread() will
* re-rate and re-select.
*/
if (list_empty(>list)) {
@@ -156,7 +177,7 @@ static void __clocksource_unstable(struct clocksource *cs)
if (cs->mark_unstable)
cs->mark_unstable(cs);
- /* kick clocksource_watchdog_work() */
+ /* kick clocksource_watchdog_kthread() */
if (finished_booting)
schedule_work(_work);
}
@@ -166,7 +187,7 @@ static void __clocksource_unstable(struct clocksource *cs)
* @cs:clocksource to be marked unstable
*
* This function is called by the x86 TSC code to mark clocksources as
unstable;
- * it defers demotion and re-selection to a work.
+ * it defers demotion and re-selection to a kthread.
*/
void clocksource_mark_unstable(struct clocksource *cs)
{
@@ -391,9 +412,7 @@ static void clocksource_dequeue_watchdog(struct clocksource
*cs)
}
}
-static void __clocksource_change_rating(struct clocksource *cs, int rating);
-
-static int __clocksource_watchdog_work(void)
+static int __clocksource_watchdog_kthread(void)
{
struct clocksource *cs, *tmp;
unsigned long flags;
@@ -418,12 +437,13 @@ static int __clocksource_watchdog_work(void)
return select;
}
-static void clocksource_watchdog_work(struct work_struct *work)
+static int clocksource_watchdog_kthread(void *data)
{
mutex_lock(_mutex);
- if (__clocksource_watchdog_work())
+ if (__clocksource_watchdog_kthread())
clocksource_select();
mutex_unlock(_mutex);
+ return 0;
}
static bool clocksource_is_watchdog(struct clocksource *cs)
@@ -442,7 +462,7 @@ static void clocksource_enqueue_watchdog(struct clocksource
*cs)
static void clocksource_select_watchdog(bool fallback) { }
static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
static inline void clocksource_resume_watchdog(void) { }
-static
[tip:timers/urgent] clocksource: Revert "Remove kthread"
Commit-ID: 760902b24960679c2e8592de3a56359d2c205731
Gitweb: https://git.kernel.org/tip/760902b24960679c2e8592de3a56359d2c205731
Author: Peter Zijlstra
AuthorDate: Wed, 5 Sep 2018 10:41:58 +0200
Committer: Thomas Gleixner
CommitDate: Thu, 6 Sep 2018 12:42:28 +0200
clocksource: Revert "Remove kthread"
I turns out that the silly spawn kthread from worker was actually needed.
clocksource_watchdog_kthread() cannot be called directly from
clocksource_watchdog_work(), because clocksource_select() calls
timekeeping_notify() which uses stop_machine(). One cannot use
stop_machine() from a workqueue() due lock inversions wrt CPU hotplug.
Revert the patch but add a comment that explain why we jump through such
apparently silly hoops.
Fixes: 7197e77abcb6 ("clocksource: Remove kthread")
Reported-by: Siegfried Metz
Signed-off-by: Peter Zijlstra (Intel)
Tested-by: Niklas Cassel
Tested-by: Kevin Shanahan
Tested-by: viktor_jaegerskuep...@freenet.de
Tested-by: Siegfried Metz
Cc: rafael.j.wyso...@intel.com
Cc: len.br...@intel.com
Cc: diego.vi...@gmail.com
Cc: rui.zh...@intel.com
Cc: bjorn.anders...@linaro.org
Link:
https://lkml.kernel.org/r/20180905084158.gr24...@hirez.programming.kicks-ass.net
---
kernel/time/clocksource.c | 40 ++--
1 file changed, 30 insertions(+), 10 deletions(-)
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index f74fb00d8064..0e6e97a01942 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -133,19 +133,40 @@ static void inline clocksource_watchdog_unlock(unsigned
long *flags)
spin_unlock_irqrestore(_lock, *flags);
}
+static int clocksource_watchdog_kthread(void *data);
+static void __clocksource_change_rating(struct clocksource *cs, int rating);
+
/*
* Interval: 0.5sec Threshold: 0.0625s
*/
#define WATCHDOG_INTERVAL (HZ >> 1)
#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
+static void clocksource_watchdog_work(struct work_struct *work)
+{
+ /*
+* We cannot directly run clocksource_watchdog_kthread() here, because
+* clocksource_select() calls timekeeping_notify() which uses
+* stop_machine(). One cannot use stop_machine() from a workqueue() due
+* lock inversions wrt CPU hotplug.
+*
+* Also, we only ever run this work once or twice during the lifetime
+* of the kernel, so there is no point in creating a more permanent
+* kthread for this.
+*
+* If kthread_run fails the next watchdog scan over the
+* watchdog_list will find the unstable clock again.
+*/
+ kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
+}
+
static void __clocksource_unstable(struct clocksource *cs)
{
cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
cs->flags |= CLOCK_SOURCE_UNSTABLE;
/*
-* If the clocksource is registered clocksource_watchdog_work() will
+* If the clocksource is registered clocksource_watchdog_kthread() will
* re-rate and re-select.
*/
if (list_empty(>list)) {
@@ -156,7 +177,7 @@ static void __clocksource_unstable(struct clocksource *cs)
if (cs->mark_unstable)
cs->mark_unstable(cs);
- /* kick clocksource_watchdog_work() */
+ /* kick clocksource_watchdog_kthread() */
if (finished_booting)
schedule_work(_work);
}
@@ -166,7 +187,7 @@ static void __clocksource_unstable(struct clocksource *cs)
* @cs:clocksource to be marked unstable
*
* This function is called by the x86 TSC code to mark clocksources as
unstable;
- * it defers demotion and re-selection to a work.
+ * it defers demotion and re-selection to a kthread.
*/
void clocksource_mark_unstable(struct clocksource *cs)
{
@@ -391,9 +412,7 @@ static void clocksource_dequeue_watchdog(struct clocksource
*cs)
}
}
-static void __clocksource_change_rating(struct clocksource *cs, int rating);
-
-static int __clocksource_watchdog_work(void)
+static int __clocksource_watchdog_kthread(void)
{
struct clocksource *cs, *tmp;
unsigned long flags;
@@ -418,12 +437,13 @@ static int __clocksource_watchdog_work(void)
return select;
}
-static void clocksource_watchdog_work(struct work_struct *work)
+static int clocksource_watchdog_kthread(void *data)
{
mutex_lock(_mutex);
- if (__clocksource_watchdog_work())
+ if (__clocksource_watchdog_kthread())
clocksource_select();
mutex_unlock(_mutex);
+ return 0;
}
static bool clocksource_is_watchdog(struct clocksource *cs)
@@ -442,7 +462,7 @@ static void clocksource_enqueue_watchdog(struct clocksource
*cs)
static void clocksource_select_watchdog(bool fallback) { }
static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
static inline void clocksource_resume_watchdog(void) { }
-static inline int
[tip:timers/urgent] clocksource: Revert "Remove kthread"
Commit-ID: 760902b24960679c2e8592de3a56359d2c205731
Gitweb: https://git.kernel.org/tip/760902b24960679c2e8592de3a56359d2c205731
Author: Peter Zijlstra
AuthorDate: Wed, 5 Sep 2018 10:41:58 +0200
Committer: Thomas Gleixner
CommitDate: Thu, 6 Sep 2018 12:42:28 +0200
clocksource: Revert "Remove kthread"
I turns out that the silly spawn kthread from worker was actually needed.
clocksource_watchdog_kthread() cannot be called directly from
clocksource_watchdog_work(), because clocksource_select() calls
timekeeping_notify() which uses stop_machine(). One cannot use
stop_machine() from a workqueue() due lock inversions wrt CPU hotplug.
Revert the patch but add a comment that explain why we jump through such
apparently silly hoops.
Fixes: 7197e77abcb6 ("clocksource: Remove kthread")
Reported-by: Siegfried Metz
Signed-off-by: Peter Zijlstra (Intel)
Tested-by: Niklas Cassel
Tested-by: Kevin Shanahan
Tested-by: viktor_jaegerskuep...@freenet.de
Tested-by: Siegfried Metz
Cc: rafael.j.wyso...@intel.com
Cc: len.br...@intel.com
Cc: diego.vi...@gmail.com
Cc: rui.zh...@intel.com
Cc: bjorn.anders...@linaro.org
Link:
https://lkml.kernel.org/r/20180905084158.gr24...@hirez.programming.kicks-ass.net
---
kernel/time/clocksource.c | 40 ++--
1 file changed, 30 insertions(+), 10 deletions(-)
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index f74fb00d8064..0e6e97a01942 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -133,19 +133,40 @@ static void inline clocksource_watchdog_unlock(unsigned
long *flags)
spin_unlock_irqrestore(_lock, *flags);
}
+static int clocksource_watchdog_kthread(void *data);
+static void __clocksource_change_rating(struct clocksource *cs, int rating);
+
/*
* Interval: 0.5sec Threshold: 0.0625s
*/
#define WATCHDOG_INTERVAL (HZ >> 1)
#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
+static void clocksource_watchdog_work(struct work_struct *work)
+{
+ /*
+* We cannot directly run clocksource_watchdog_kthread() here, because
+* clocksource_select() calls timekeeping_notify() which uses
+* stop_machine(). One cannot use stop_machine() from a workqueue() due
+* lock inversions wrt CPU hotplug.
+*
+* Also, we only ever run this work once or twice during the lifetime
+* of the kernel, so there is no point in creating a more permanent
+* kthread for this.
+*
+* If kthread_run fails the next watchdog scan over the
+* watchdog_list will find the unstable clock again.
+*/
+ kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
+}
+
static void __clocksource_unstable(struct clocksource *cs)
{
cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
cs->flags |= CLOCK_SOURCE_UNSTABLE;
/*
-* If the clocksource is registered clocksource_watchdog_work() will
+* If the clocksource is registered clocksource_watchdog_kthread() will
* re-rate and re-select.
*/
if (list_empty(>list)) {
@@ -156,7 +177,7 @@ static void __clocksource_unstable(struct clocksource *cs)
if (cs->mark_unstable)
cs->mark_unstable(cs);
- /* kick clocksource_watchdog_work() */
+ /* kick clocksource_watchdog_kthread() */
if (finished_booting)
schedule_work(_work);
}
@@ -166,7 +187,7 @@ static void __clocksource_unstable(struct clocksource *cs)
* @cs:clocksource to be marked unstable
*
* This function is called by the x86 TSC code to mark clocksources as
unstable;
- * it defers demotion and re-selection to a work.
+ * it defers demotion and re-selection to a kthread.
*/
void clocksource_mark_unstable(struct clocksource *cs)
{
@@ -391,9 +412,7 @@ static void clocksource_dequeue_watchdog(struct clocksource
*cs)
}
}
-static void __clocksource_change_rating(struct clocksource *cs, int rating);
-
-static int __clocksource_watchdog_work(void)
+static int __clocksource_watchdog_kthread(void)
{
struct clocksource *cs, *tmp;
unsigned long flags;
@@ -418,12 +437,13 @@ static int __clocksource_watchdog_work(void)
return select;
}
-static void clocksource_watchdog_work(struct work_struct *work)
+static int clocksource_watchdog_kthread(void *data)
{
mutex_lock(_mutex);
- if (__clocksource_watchdog_work())
+ if (__clocksource_watchdog_kthread())
clocksource_select();
mutex_unlock(_mutex);
+ return 0;
}
static bool clocksource_is_watchdog(struct clocksource *cs)
@@ -442,7 +462,7 @@ static void clocksource_enqueue_watchdog(struct clocksource
*cs)
static void clocksource_select_watchdog(bool fallback) { }
static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
static inline void clocksource_resume_watchdog(void) { }
-static inline int
