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Date: Wed, 2 May 2018 15:53:12 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org, diego.viola@...il.com,
len.brown@...el.com, rjw@...ysocki.net, rui.zhang@...el.com,
stable@...nel.org
Subject: Re: [PATCH v2 2/7] clocksource: Allow clocksource_mark_unstable() on
unregisered clocksources
On Wed, May 02, 2018 at 03:35:53PM +0200, Thomas Gleixner wrote:
> On Mon, 30 Apr 2018, Peter Zijlstra wrote:
> > --- a/kernel/time/clocksource.c
> > +++ b/kernel/time/clocksource.c
> > @@ -119,6 +119,16 @@ static DEFINE_SPINLOCK(watchdog_lock);
> > static int watchdog_running;
> > static atomic_t watchdog_reset_pending;
> >
> > +static void inline clocksource_watchdog_lock(unsigned long *flags)
> > +{
> > + spin_lock_irqsave(&watchdog_lock, *flags);
> > +}
> > +
> > +static void inline clocksource_watchdog_unlock(unsigned long *flags)
> > +{
> > + spin_unlock_irqrestore(&watchdog_lock, *flags);
> > +}
>
> I can see why you made that wrapper, but where are the stubs for
> !CONFIG_CLOCKSOURCE_WATCHDOG?
Whoops ;-)
---
Subject: clocksource: Allow clocksource_mark_unstable() on unregisered clocksources
From: Peter Zijlstra <peterz@...radead.org>
Date: Mon Apr 23 17:28:55 CEST 2018
Because of how the code flips between tsc-early and tsc clocksources
it might need to mark one or both unstable. The current code in
mark_tsc_unstable() only worked because previously it registered the
tsc clocksource once and then never touched it.
Since it now unregisters the tsc-early clocksource, it needs to know
if a clocksource got unregistered and the current cs->mult test
doesn't work for that. Instead use list_empty(&cs->list) to test for
registration.
Furthermore, since clocksource_mark_unstable() needs to place the cs
on the wd_list, it links the cs->list and cs->wd_list serialization.
It must not see a clocsource registered (!empty cs->list) but already
past dequeue_watchdog(). So place {en,de}queue{,_watchdog}() under the
same lock.
Provided cs->list is initialized to empty, this then allows us to
unconditionally use clocksource_mark_unstable(), regardless of the
registration state.
Cc: stable@...nel.org
Tested-by: Diego Viola <diego.viola@...il.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
kernel/time/clocksource.c | 50 +++++++++++++++++++++++++++++++---------------
1 file changed, 34 insertions(+), 16 deletions(-)
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -119,6 +119,16 @@ static DEFINE_SPINLOCK(watchdog_lock);
static int watchdog_running;
static atomic_t watchdog_reset_pending;
+static void inline clocksource_watchdog_lock(unsigned long *flags)
+{
+ spin_lock_irqsave(&watchdog_lock, *flags);
+}
+
+static void inline clocksource_watchdog_unlock(unsigned long *flags)
+{
+ spin_unlock_irqrestore(&watchdog_lock, *flags);
+}
+
static int clocksource_watchdog_kthread(void *data);
static void __clocksource_change_rating(struct clocksource *cs, int rating);
@@ -142,6 +152,9 @@ static void __clocksource_unstable(struc
cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
cs->flags |= CLOCK_SOURCE_UNSTABLE;
+ if (list_empty(&cs->list))
+ return;
+
if (cs->mark_unstable)
cs->mark_unstable(cs);
@@ -164,7 +177,7 @@ void clocksource_mark_unstable(struct cl
spin_lock_irqsave(&watchdog_lock, flags);
if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
- if (list_empty(&cs->wd_list))
+ if (!list_empty(&cs->list) && list_empty(&cs->wd_list))
list_add(&cs->wd_list, &watchdog_list);
__clocksource_unstable(cs);
}
@@ -319,9 +332,6 @@ static void clocksource_resume_watchdog(
static void clocksource_enqueue_watchdog(struct clocksource *cs)
{
- unsigned long flags;
-
- spin_lock_irqsave(&watchdog_lock, flags);
if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
/* cs is a clocksource to be watched. */
list_add(&cs->wd_list, &watchdog_list);
@@ -331,7 +341,6 @@ static void clocksource_enqueue_watchdog
if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
}
- spin_unlock_irqrestore(&watchdog_lock, flags);
}
static void clocksource_select_watchdog(bool fallback)
@@ -373,9 +382,6 @@ static void clocksource_select_watchdog(
static void clocksource_dequeue_watchdog(struct clocksource *cs)
{
- unsigned long flags;
-
- spin_lock_irqsave(&watchdog_lock, flags);
if (cs != watchdog) {
if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
/* cs is a watched clocksource. */
@@ -384,21 +390,19 @@ static void clocksource_dequeue_watchdog
clocksource_stop_watchdog();
}
}
- spin_unlock_irqrestore(&watchdog_lock, flags);
}
static int __clocksource_watchdog_kthread(void)
{
struct clocksource *cs, *tmp;
unsigned long flags;
- LIST_HEAD(unstable);
int select = 0;
spin_lock_irqsave(&watchdog_lock, flags);
list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
list_del_init(&cs->wd_list);
- list_add(&cs->wd_list, &unstable);
+ __clocksource_change_rating(cs, 0);
select = 1;
}
if (cs->flags & CLOCK_SOURCE_RESELECT) {
@@ -410,11 +414,6 @@ static int __clocksource_watchdog_kthrea
clocksource_stop_watchdog();
spin_unlock_irqrestore(&watchdog_lock, flags);
- /* Needs to be done outside of watchdog lock */
- list_for_each_entry_safe(cs, tmp, &unstable, wd_list) {
- list_del_init(&cs->wd_list);
- __clocksource_change_rating(cs, 0);
- }
return select;
}
@@ -447,6 +446,9 @@ static inline int __clocksource_watchdog
static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
void clocksource_mark_unstable(struct clocksource *cs) { }
+static void inline clocksource_watchdog_lock(unsigned long *flags) { }
+static void inline clocksource_watchdog_unlock(unsigned long *flags) { }
+
#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
/**
@@ -779,14 +781,19 @@ EXPORT_SYMBOL_GPL(__clocksource_update_f
*/
int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
{
+ unsigned long flags;
/* Initialize mult/shift and max_idle_ns */
__clocksource_update_freq_scale(cs, scale, freq);
/* Add clocksource to the clocksource list */
mutex_lock(&clocksource_mutex);
+
+ clocksource_watchdog_lock(&flags);
clocksource_enqueue(cs);
clocksource_enqueue_watchdog(cs);
+ clocksource_watchdog_unlock(&flags);
+
clocksource_select();
clocksource_select_watchdog(false);
mutex_unlock(&clocksource_mutex);
@@ -808,8 +815,13 @@ static void __clocksource_change_rating(
*/
void clocksource_change_rating(struct clocksource *cs, int rating)
{
+ unsigned long flags;
+
mutex_lock(&clocksource_mutex);
+ clocksource_watchdog_lock(&flags);
__clocksource_change_rating(cs, rating);
+ clocksource_watchdog_unlock(&flags);
+
clocksource_select();
clocksource_select_watchdog(false);
mutex_unlock(&clocksource_mutex);
@@ -821,6 +833,8 @@ EXPORT_SYMBOL(clocksource_change_rating)
*/
static int clocksource_unbind(struct clocksource *cs)
{
+ unsigned long flags;
+
if (clocksource_is_watchdog(cs)) {
/* Select and try to install a replacement watchdog. */
clocksource_select_watchdog(true);
@@ -834,8 +848,12 @@ static int clocksource_unbind(struct clo
if (curr_clocksource == cs)
return -EBUSY;
}
+
+ clocksource_watchdog_lock(&flags);
clocksource_dequeue_watchdog(cs);
list_del_init(&cs->list);
+ clocksource_watchdog_unlock(&flags);
+
return 0;
}
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