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Date: Tue, 27 Mar 2007 09:46:40 -0700
From: Jeremy Fitzhardinge <jeremy@...p.org>
To: Prarit Bhargava <prarit@...hat.com>
CC: linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
clalance@...hat.com, mingo@...hat.com, davej@...hat.com,
Thilo.Cestonaro.external@...itsu-siemens.com
Subject: Re: [PATCH]: Fix bogus softlockup warning with sysrq-t
Prarit Bhargava wrote:
> I think that's a good idea -- I'll propose an add on patch to fix the
> sysrq-t case ...
I'm working on this patch at the moment. I'm just wondering what
happens if you do a global re-enable while a CPU is locally disabled. I
think it won't matter; it will end up in the "enabled but need to update
timestamp" state, and the next time it gets a timer tick, it will simply
update the timestamp and carry on.
(This is relative to the other two softlockup patches, but modified
since I posted them.)
J
diff -r 4c81d8cafb67 drivers/char/sysrq.c
--- a/drivers/char/sysrq.c Tue Mar 27 01:16:07 2007 -0700
+++ b/drivers/char/sysrq.c Tue Mar 27 01:18:05 2007 -0700
@@ -408,6 +408,8 @@ void __handle_sysrq(int key, struct tty_
int i;
unsigned long flags;
+ softlockup_global_disable();
+
spin_lock_irqsave(&sysrq_key_table_lock, flags);
orig_log_level = console_loglevel;
console_loglevel = 7;
@@ -445,6 +447,8 @@ void __handle_sysrq(int key, struct tty_
console_loglevel = orig_log_level;
}
spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
+
+ softlockup_global_enable();
}
/*
diff -r 4c81d8cafb67 include/linux/sched.h
--- a/include/linux/sched.h Tue Mar 27 01:16:07 2007 -0700
+++ b/include/linux/sched.h Tue Mar 27 01:18:05 2007 -0700
@@ -235,6 +235,8 @@ extern void softlockup_tick(void);
extern void softlockup_tick(void);
extern void softlockup_enable(void);
extern void softlockup_disable(void);
+extern void softlockup_global_enable(void);
+extern void softlockup_global_disable(void);
extern void spawn_softlockup_task(void);
extern void touch_softlockup_watchdog(void);
#else
@@ -245,6 +247,12 @@ static inline void softlockup_enable(voi
{
}
static inline void softlockup_disable(void)
+{
+}
+static inline void softlockup_global_enable(void)
+{
+}
+static inline void softlockup_global_disable(void)
{
}
static inline void spawn_softlockup_task(void)
diff -r 4c81d8cafb67 kernel/softlockup.c
--- a/kernel/softlockup.c Tue Mar 27 01:16:07 2007 -0700
+++ b/kernel/softlockup.c Tue Mar 27 01:18:05 2007 -0700
@@ -17,10 +17,16 @@
static DEFINE_SPINLOCK(print_lock);
+enum enable {
+ SL_OFF = 0, /* disabled */
+ SL_UPDATE, /* enabled, but timestamp old */
+ SL_ON, /* enabled */
+};
+
static DEFINE_PER_CPU(unsigned long long, touch_timestamp);
static DEFINE_PER_CPU(unsigned long long, print_timestamp);
static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
-static DEFINE_PER_CPU(int, enabled);
+static DEFINE_PER_CPU(enum enable, enabled);
static int did_panic = 0;
@@ -39,6 +45,8 @@ void touch_softlockup_watchdog(void)
void touch_softlockup_watchdog(void)
{
__raw_get_cpu_var(touch_timestamp) = sched_clock();
+ barrier(); /* update timestamp before enable */
+ __raw_get_cpu_var(enabled) = SL_ON;
}
EXPORT_SYMBOL(touch_softlockup_watchdog);
@@ -57,13 +65,27 @@ void softlockup_enable(void)
void softlockup_enable(void)
{
touch_softlockup_watchdog();
- barrier(); /* update timestamp before enable */
- __get_cpu_var(enabled) = 1;
}
void softlockup_disable(void)
{
- __get_cpu_var(enabled) = 0;
+ __get_cpu_var(enabled) = SL_OFF;
+}
+
+void softlockup_global_enable()
+{
+ unsigned cpu;
+
+ for_each_online_cpu(cpu)
+ per_cpu(enabled, cpu) = SL_UPDATE;
+}
+
+void softlockup_global_disable()
+{
+ unsigned cpu;
+
+ for_each_online_cpu(cpu)
+ per_cpu(enabled, cpu) = SL_OFF;
}
/*
@@ -79,9 +101,19 @@ void softlockup_tick(void)
touch_timestamp = get_timestamp(&__get_cpu_var(touch_timestamp));
- /* return if not enabled */
- if (!__get_cpu_var(enabled))
- return;
+ switch(__get_cpu_var(enabled)) {
+ case SL_OFF:
+ /* not enabled */
+ return;
+
+ case SL_UPDATE:
+ /* update timestamp */
+ touch_softlockup_watchdog();
+ break;
+
+ case SL_ON:
+ break;
+ }
print_timestamp = __get_cpu_var(print_timestamp);
-
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