From 908b82659598cb1e96abc5f28539a66dfd427643 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Fri, 2 Mar 2012 10:36:57 -0500 Subject: cpu: Make hotplug.lock a "sleeping" spinlock on RT 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 Cc: Carsten Emde Cc: John Kacur Cc: Peter Zijlstra Cc: Clark Williams 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 --- kernel/cpu.c | 31 ++++++++++++++++++++++--------- 1 file changed, 22 insertions(+), 9 deletions(-) diff --git a/kernel/cpu.c b/kernel/cpu.c index fa4083478d75..c25b5ffb63e2 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -46,7 +46,12 @@ 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. @@ -58,6 +63,14 @@ static struct { .refcount = 0, }; +#ifdef CONFIG_PREEMPT_RT_FULL +# define hotplug_lock() spin_lock(&cpu_hotplug.lock) +# define hotplug_unlock() spin_unlock(&cpu_hotplug.lock) +#else +# define hotplug_lock() mutex_lock(&cpu_hotplug.lock) +# define hotplug_lock() mutex_unlock(&cpu_hotplug.lock) +#endif + struct hotplug_pcp { struct task_struct *unplug; int refcount; @@ -87,8 +100,8 @@ retry: return; } preempt_enable(); - mutex_lock(&cpu_hotplug.lock); - mutex_unlock(&cpu_hotplug.lock); + hotplug_lock(); + hotplug_unlock(); preempt_disable(); goto retry; } @@ -161,9 +174,9 @@ 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); @@ -172,10 +185,10 @@ void put_online_cpus(void) { if (cpu_hotplug.active_writer == current) return; - mutex_lock(&cpu_hotplug.lock); + hotplug_lock(); 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); @@ -207,11 +220,11 @@ 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(); } } @@ -219,7 +232,7 @@ static void cpu_hotplug_begin(void) static void cpu_hotplug_done(void) { cpu_hotplug.active_writer = NULL; - mutex_unlock(&cpu_hotplug.lock); + hotplug_unlock(); } #else /* #if CONFIG_HOTPLUG_CPU */ -- cgit v1.2.3