Re: [PATCH] Fixes for RCU handling of task_struct

[Nick Piggin <nickpiggin@yahoo.com.au>]

Andrew Morton wrote:

>>+static inline int get_task_struct_rcu(struct task_struct *t)
>>+{
>>+	int oldusage;
>>+
>>+	do {
>>+		oldusage = atomic_read(&t->usage);
>>+		if (oldusage == 0) {
>>+			return 0;
>>+		}
>>+	} while (cmpxchg(&t->usage.counter,
>>+		 oldusage, oldusage + 1) != oldusage);
>>+	return 1;
>>+}
> 
> 
> arm (at least) does not implement cmpxchg.
> 

Yes, and using atomic_t.counter in generic code is ugly, albeit
compatible with all current implementations.

> I think Nick is working on patches which implement cmpxchg on all
> architectures?
> 

Yes, it is basically ready to go.

-- 
SUSE Labs, Novell Inc.

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