linux-kernel - Re: [PATCH] seqlock: fix raw_read_seqcount

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Message-ID: <20160522104827.GP3193@twins.programming.kicks-ass.net>
Date:	Sun, 22 May 2016 12:48:27 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH] seqlock: fix raw_read_seqcount_latch()

On Sat, May 21, 2016 at 11:14:49PM +0300, Alexey Dobriyan wrote:
> lockless_dereference() is supposed to take pointer not integer.

Urgh :/

Is there any way we can make lockless_dereference() issue a warning if
we don't feed it a pointer?

Would something like so work? All pointer types should silently cast to
void * while integer (and others) should refuse to.

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index b5ff9881bef8..8886de704d33 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -544,6 +544,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
  */
 #define lockless_dereference(p) \
 ({ \
+ 	__maybe_unused void * _________p2 = p; \
 	typeof(p) _________p1 = READ_ONCE(p); \
 	smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
 	(_________p1); \