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Date: Tue, 1 May 2012 10:12:38 +1000 From: Paul Mackerras <paulus@...ba.org> To: linux-kernel@...r.kernel.org Cc: Rusty Russell <rusty@...tcorp.com.au> Subject: get/put_online_cpus documentation wrong? In Documentation/cpu-hotplug.txt it says: " #include <linux/cpu.h> get_online_cpus() and put_online_cpus(): The above calls are used to inhibit cpu hotplug operations. While the cpu_hotplug.refcount is non zero, the cpu_online_mask will not change. If you merely need to avoid cpus going away, you could also use preempt_disable() and preempt_enable() for those sections. Just remember the critical section cannot call any function that can sleep or schedule this process away." That last statement doesn't seem like it can be correct, given that get_online_cpus and put_online_cpus both do a mutex_lock(), which can sleep. So, is that statement still correct? What would happen if a process did sleep after doing get_online_cpus()? Also, get/put_online_cpus doing mutex_lock() implies that one should not call them in atomic context, e.g. while holding a spinlock, which could usefully be mentioned in cpu-hotplug.txt. I'm happy to do a patch to update cpu-hotplug.txt once it's clear what the actual constraints are. Paul. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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