lkml.org 
[lkml]   [2010]   [Apr]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH tip/urgent] rcu: add rcu_access_pointer and rcu_dereference_protected
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


\
 
 \ /
  Last update: 2010-04-08 01:03    [W:0.091 / U:0.920 seconds]
©2003-2014 Jasper Spaans. Advertise on this site