linux-kernel - Re: [PATCH] perf_counter: more barrier in blank weak function

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Message-Id: <20081227150534.F472.KOSAKI.MOTOHIRO@jp.fujitsu.com>
Date:	Sat, 27 Dec 2008 15:07:06 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	kosaki.motohiro@...fujitsu.com, Sam Ravnborg <sam@...nborg.org>,
	David Howells <dhowells@...hat.com>, mingo@...e.hu,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	mel@....ul.ie
Subject: Re: [PATCH] perf_counter: more barrier in blank weak function

> 
> Impact: fix panic possible panic etc
> 
> some compiler seems to inline the weak global function if no line in it
> 
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> 
> diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
> index d7a79f3..37f7716 100644
> --- a/kernel/perf_counter.c
> +++ b/kernel/perf_counter.c
> @@ -45,8 +45,8 @@ hw_perf_counter_init(struct perf_counter *counter)
>  }
>  
>  u64 __weak hw_perf_save_disable(void)		{ return 0; }
> -void __weak hw_perf_restore(u64 ctrl)		{ }
> -void __weak hw_perf_counter_setup(void)		{ }
> +void __weak hw_perf_restore(u64 ctrl)		{ barrier(); }
> +void __weak hw_perf_counter_setup(void)		{ barrier(); }

We need comment into the function.
I expect anyone think "hm, this barrier() is meaningless. let's cleanup." in the future.
we should avoid it.



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