Re: [GIT PULL rcu/next] RCU commits for 3.1

[Eric Dumazet]

Le lundi 07 novembre 2011 Ã 14:24 +0000, Stephane Eranian a Ãcrit :
> Hi,
> 
> Some second thoughts on this.
> 
> We get the warning because:
> 
> #define task_subsys_state_check(task, subsys_id, __c)                   \
>         rcu_dereference_check(task->cgroups->subsys[subsys_id],         \
>                               lockdep_is_held(&task->alloc_lock) ||     \
>                               cgroup_lock_is_held() || (__c))
> 
> 
> In other words, we need the alloc_lock held.
> 
> What I don't quite understand in your patch in the connection
> between rcu and this particular task lock. Unless holding
> the rcu read lock implies you necessarily hold the alloc_lock.
> 
> Can you explain?

#define rcu_dereference_check(p, c) \
	__rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)

So if you hold rcu_read_lock(), (c) is not checked/asserted.



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