Re: [PATCH tip/urgent] rcu: add rcu_access_pointer and rcu_dereference_protected

From: David Howells
Date: Wed Apr 07 2010 - 13:21:56 EST

Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> wrote:

> In other cases, there will be a reference counter or a "not yet fully
> initialized" flag that can (and should) be tested.

Why would you be using rcu_access_pointer() there? Why wouldn't you be using

Also, one other thing: Should the default versions of these functions make
some reference to 'c' to prevent compiler warnings? Should:

#define rcu_dereference_check(p, c) rcu_dereference_raw(p)

for example, be:

#define rcu_dereference_check(p, c) \
({ \
if (1 || !(c)) \
rcu_dereference_raw(p); \

I'm not sure it's necessary, but it's possible to envisage a situation where
someone calculates something specifically for use in 'c', which will cause an
warning from the compiler if c isn't then checked.

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