Date: Thu, 4 Jan 2018 15:13:07 -0800
From: Matthew Wilcox <willy@infradead.org>
To: Rao Shoaib <rao.shoaib@oracle.com>
Cc: Boqun Feng <boqun.feng@gmail.com>, linux-kernel@vger.kernel.org,
        paulmck@linux.vnet.ibm.com, brouer@redhat.com, linux-mm@kvack.org
Subject: Re: [PATCH 1/2] Move kfree_call_rcu() to slab_common.c
Message-ID: <20180104231307.GA794@bombadil.infradead.org>
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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.