linux-kernel - Re: [PATCH 1/2] Move kfree_call_rcu() to slab

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Date:   Thu, 4 Jan 2018 16:07:07 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Joe Perches <joe@...ches.com>, Rao Shoaib <rao.shoaib@...cle.com>,
        Boqun Feng <boqun.feng@...il.com>,
        linux-kernel@...r.kernel.org, brouer@...hat.com, linux-mm@...ck.org
Subject: Re: [PATCH 1/2] Move kfree_call_rcu() to slab_common.c

On Thu, Jan 04, 2018 at 03:47:32PM -0800, Paul E. McKenney wrote:
> 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?

I think checkpatch is confused by the '*' in the typeof argument:

$ git diff |./scripts/checkpatch.pl --strict
CHECK: Macro argument reuse 'ptr' - possible side-effects?
#29: FILE: include/linux/rcupdate.h:896:
+#define kfree_rcu(ptr, rcu_head)                                        \
+	__kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))

If one removes the '*', the warning goes away.

I'm no perlista, but Joe, would this regexp modification make sense?

+++ b/scripts/checkpatch.pl
@@ -4957,7 +4957,7 @@ sub process {
                                next if ($arg =~ /\.\.\./);
                                next if ($arg =~ /^type$/i);
                                my $tmp_stmt = $define_stmt;
-                               $tmp_stmt =~ s/\b(typeof|__typeof__|__builtin\w+|typecheck\s*\(\s*$Type\s*,|\#+)\s*\(*\s*$arg\s*\)*\b//g;
+                               $tmp_stmt =~ s/\b(typeof|__typeof__|__builtin\w+|typecheck\s*\(\s*$Type\s*,|\#+)\s*\(*\**\(*\s*$arg\s*\)*\b//g;
                                $tmp_stmt =~ s/\#+\s*$arg\b//g;
                                $tmp_stmt =~ s/\b$arg\s*\#\#//g;
                                my $use_cnt = $tmp_stmt =~ s/\b$arg\b//g;