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[PATCH] cpu hotplug: fix locking in cpufreq drivers

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When calling target drivers to set frequency, we take cpucontrol lock.
When we modified the code to accomodate CPU hotplug, there was an attempt
to take a double lock of cpucontrol leading to a deadlock.  Since the
current thread context is already holding the cpucontrol lock, we dont need
to make another attempt to acquire it.

Now we leave a trace in current->flags indicating current thread already is
under cpucontrol lock held, so we dont attempt to do this another time.

Thanks to Andrew Morton for the beating:-)

From: Brice Goglin <Brice.Goglin@ens-lyon.org>

  Build fix

(akpm: this patch is still unpleasant.  Ashok continues to look for a cleaner
solution, doesn't he?  ;))

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Brice Goglin <Brice.Goglin@ens-lyon.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Ashok Raj 2005-11-08 21:34:24 -08:00 • committed by Linus Torvalds
parent 330d57fb98
commit 90d45d17f3
4 changed files with 49 additions and 14 deletions
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5
include/linux/cpu.h
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@ -42,6 +42,7 @@ struct notifier_block;
/* Need to know about CPUs going up/down? */
extern int register_cpu_notifier(struct notifier_block *nb);
extern void unregister_cpu_notifier(struct notifier_block *nb);
extern int current_in_cpu_hotplug(void);
int cpu_up(unsigned int cpu);
@ -54,6 +55,10 @@ static inline int register_cpu_notifier(struct notifier_block *nb)
static inline void unregister_cpu_notifier(struct notifier_block *nb)
{
}
static inline int current_in_cpu_hotplug(void)
{
return 0;
}
#endif /* CONFIG_SMP */
extern struct sysdev_class cpu_sysdev_class;