linux-kernel - Re: rcu alignment warning tripping on m68k

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Date:	Fri, 30 May 2014 11:29:41 +1000
From:	Greg Ungerer <gerg@...inux.org>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
CC:	Linux Kernel Development <linux-kernel@...r.kernel.org>,
	Linux/m68k <linux-m68k@...r.kernel.org>
Subject: Re: rcu alignment warning tripping on m68k

On 29/05/14 23:11, One Thousand Gnomes wrote:
> On Thu, 29 May 2014 12:08:32 +1000
> Greg Ungerer <gerg@...inux.org> wrote:
> 
>> Hi All,
>>
>> Inside kernel/rcy/tree.c in __call_rcu() it does an alignment check on
>> the head pointer passed in. This trips on m68k systems, because they only
>> need alignment of 32bit quantities to 16bit boundaries.
> 
> __alignof perhaps ?

That might do. Change then becomes something like:

--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2467,7 +2467,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_
        unsigned long flags;
        struct rcu_data *rdp;
 
-       WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */
+       WARN_ON_ONCE((unsigned long)head & (__alignof__(head) - 1)); /* Misaligned rcu_head! */
        if (debug_rcu_head_queue(head)) {
                /* Probable double call_rcu(), so leak the callback. */
                ACCESS_ONCE(head->func) = rcu_leak_callback;

Thanks
Greg


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