| Subject: cpu: Make hotplug.lock a "sleeping" spinlock on RT |
| From: Steven Rostedt <rostedt@goodmis.org> |
| Date: Fri, 02 Mar 2012 10:36:57 -0500 |
| |
| Tasks can block on hotplug.lock in pin_current_cpu(), but their state |
| might be != RUNNING. So the mutex wakeup will set the state |
| unconditionally to RUNNING. That might cause spurious unexpected |
| wakeups. We could provide a state preserving mutex_lock() function, |
| but this is semantically backwards. So instead we convert the |
| hotplug.lock() to a spinlock for RT, which has the state preserving |
| semantics already. |
| |
| Signed-off-by: Steven Rostedt <rostedt@goodmis.org> |
| Cc: Carsten Emde <C.Emde@osadl.org> |
| Cc: John Kacur <jkacur@redhat.com> |
| Cc: Peter Zijlstra <peterz@infradead.org> |
| Cc: Clark Williams <clark.williams@gmail.com> |
| Cc: stable-rt@vger.kernel.org |
| Link: http://lkml.kernel.org/r/1330702617.25686.265.camel@gandalf.stny.rr.com |
| Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
| --- |
| kernel/cpu.c | 35 ++++++++++++++++++++++++++--------- |
| 1 file changed, 26 insertions(+), 9 deletions(-) |
| |
| --- a/kernel/cpu.c |
| +++ b/kernel/cpu.c |
| @@ -51,7 +51,12 @@ static int cpu_hotplug_disabled; |
| |
| static struct { |
| struct task_struct *active_writer; |
| +#ifdef CONFIG_PREEMPT_RT_FULL |
| + /* Makes the lock keep the task's state */ |
| + spinlock_t lock; |
| +#else |
| struct mutex lock; /* Synchronizes accesses to refcount, */ |
| +#endif |
| /* |
| * Also blocks the new readers during |
| * an ongoing cpu hotplug operation. |
| @@ -59,10 +64,22 @@ static struct { |
| int refcount; |
| } cpu_hotplug = { |
| .active_writer = NULL, |
| +#ifdef CONFIG_PREEMPT_RT_FULL |
| + .lock = __SPIN_LOCK_UNLOCKED(cpu_hotplug.lock), |
| +#else |
| .lock = __MUTEX_INITIALIZER(cpu_hotplug.lock), |
| +#endif |
| .refcount = 0, |
| }; |
| |
| +#ifdef CONFIG_PREEMPT_RT_FULL |
| +# define hotplug_lock() rt_spin_lock(&cpu_hotplug.lock) |
| +# define hotplug_unlock() rt_spin_unlock(&cpu_hotplug.lock) |
| +#else |
| +# define hotplug_lock() mutex_lock(&cpu_hotplug.lock) |
| +# define hotplug_unlock() mutex_unlock(&cpu_hotplug.lock) |
| +#endif |
| + |
| struct hotplug_pcp { |
| struct task_struct *unplug; |
| int refcount; |
| @@ -92,8 +109,8 @@ retry: |
| return; |
| } |
| preempt_enable(); |
| - mutex_lock(&cpu_hotplug.lock); |
| - mutex_unlock(&cpu_hotplug.lock); |
| + hotplug_lock(); |
| + hotplug_unlock(); |
| preempt_disable(); |
| goto retry; |
| } |
| @@ -165,9 +182,9 @@ void get_online_cpus(void) |
| might_sleep(); |
| if (cpu_hotplug.active_writer == current) |
| return; |
| - mutex_lock(&cpu_hotplug.lock); |
| + hotplug_lock(); |
| cpu_hotplug.refcount++; |
| - mutex_unlock(&cpu_hotplug.lock); |
| + hotplug_unlock(); |
| |
| } |
| EXPORT_SYMBOL_GPL(get_online_cpus); |
| @@ -176,14 +193,14 @@ void put_online_cpus(void) |
| { |
| if (cpu_hotplug.active_writer == current) |
| return; |
| - mutex_lock(&cpu_hotplug.lock); |
| |
| + hotplug_lock(); |
| if (WARN_ON(!cpu_hotplug.refcount)) |
| cpu_hotplug.refcount++; /* try to fix things up */ |
| |
| if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer)) |
| wake_up_process(cpu_hotplug.active_writer); |
| - mutex_unlock(&cpu_hotplug.lock); |
| + hotplug_unlock(); |
| |
| } |
| EXPORT_SYMBOL_GPL(put_online_cpus); |
| @@ -215,11 +232,11 @@ static void cpu_hotplug_begin(void) |
| cpu_hotplug.active_writer = current; |
| |
| for (;;) { |
| - mutex_lock(&cpu_hotplug.lock); |
| + hotplug_lock(); |
| if (likely(!cpu_hotplug.refcount)) |
| break; |
| __set_current_state(TASK_UNINTERRUPTIBLE); |
| - mutex_unlock(&cpu_hotplug.lock); |
| + hotplug_unlock(); |
| schedule(); |
| } |
| } |
| @@ -227,7 +244,7 @@ static void cpu_hotplug_begin(void) |
| static void cpu_hotplug_done(void) |
| { |
| cpu_hotplug.active_writer = NULL; |
| - mutex_unlock(&cpu_hotplug.lock); |
| + hotplug_unlock(); |
| } |
| |
| /* |