Messages in this thread | | | Date | Thu, 4 Jan 2018 15:47:32 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 1/2] Move kfree_call_rcu() to slab_common.c |
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On Thu, Jan 04, 2018 at 03:13:07PM -0800, Matthew Wilcox wrote: > On Thu, Jan 04, 2018 at 02:18:50PM -0800, Rao Shoaib wrote: > > > > > > +#define kfree_rcu(ptr, rcu_head_name) \ > > > > > > + do { \ > > > > > > + typeof(ptr) __ptr = ptr; \ > > > > > > + unsigned long __off = offsetof(typeof(*(__ptr)), \ > > > > > > + rcu_head_name); \ > > > > > > + struct rcu_head *__rptr = (void *)__ptr + __off; \ > > > > > > + __kfree_rcu(__rptr, __off); \ > > > > > > + } while (0) > > > > > why do you want to open code this? > > > But why are you changing this macro at all? If it was to avoid the > > > double-mention of "ptr", then you haven't done that. > > I have -- I do not get the error because ptr is being assigned only one. If > > you have a better way than let me know and I will be happy to make the > > change. > > But look at the original: > > #define kfree_rcu(ptr, rcu_head) \ > __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head)) > ^^^ ^^^ > > versus your version: > > +#define kfree_rcu(ptr, rcu_head_name) \ > + do { \ > + typeof(ptr) __ptr = ptr; \ > ^^^ ^^^ > + unsigned long __off = offsetof(typeof(*(__ptr)), \ > + rcu_head_name); \ > + struct rcu_head *__rptr = (void *)__ptr + __off; \ > + __kfree_rcu(__rptr, __off); \ > + } while (0) > > I don't see the difference.
I was under the impression that typeof did not actually evaluate its argument, but rather only returned its type. And there are a few macros with this pattern in mainline.
Or am I confused about what typeof does?
Thanx, Paul
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