Messages in this thread | | | Date | Wed, 7 Apr 2010 16:00:09 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/urgent] rcu: add rcu_access_pointer and rcu_dereference_protected |
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On Wed, Apr 07, 2010 at 06:20:48PM +0100, David Howells wrote: > Paul E. McKenney <paulmck@linux.vnet.ibm.com> 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 > rcu_dereference_protected()?
Excellent question. I am writing up the documentation now, and will either (1) have a good use case or (2) remove the condition.
> 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.
I did try this. The problem is that it breaks the build for non-lockdep configurations due to the lockdep-check primitives not being defined. :-(
Thanx, Paul
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