On Mon, 22 Apr 2013 13:47:22 +0800 liguang <lig.f...@cn.fujitsu.com> wrote:
> originally, 'data->flags = CSD_FLAG_LOCK',
> and we use 'data->flags &= ~CSD_FLAG_LOCK'
> for csd_unlock, they are not symmetrix operations
> so use '|=' instead of '='.
> though, now data->flags only hold CSD_FLAG_LOCK,
> it's not so meaningful to use '|=' to set 1 bit,
> and '&= ~' to clear 1 bit.
>
> Signed-off-by: liguang <lig.f...@cn.fujitsu.com>
> ---
> kernel/smp.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/smp.c b/kernel/smp.c
> index 1818dc0..2d5deb4 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -109,7 +109,7 @@ static void csd_lock_wait(struct call_single_data *data)
> static void csd_lock(struct call_single_data *data)
> {
> csd_lock_wait(data);
> - data->flags = CSD_FLAG_LOCK;
> + data->flags |= CSD_FLAG_LOCK;
>
> /*
call_single_data.flags is in fact presently a boolean - we only use one
bit in that word. We could remove all the &=, |=, & and | operations
on call_single_data.flags and treat it as a boolean. That would
probably result in faster and smaller code.
But leaving the other 31 bits alone and reserved-for-future-use is not
a bad thing. But if we're going to do that we should do it consistently.
I rewrote your changelog ;)
From: liguang <lig.f...@cn.fujitsu.com>
Subject: kernel/smp.c: use '|=' for csd_lock
csd_lock() uses assignment to data->flags rather than |=. That is not
buggy at present because only one bit (CSD_FLAG_LOCK) is defined in
call_single_data.flags.
But it will become buggy if we later add another flag, so fix it now.
Signed-off-by: liguang <lig.f...@cn.fujitsu.com>
Cc: Peter Zijlstra <a.p.zijls...@chello.nl>
Cc: Oleg Nesterov <o...@redhat.com>
Cc: Ingo Molnar <mi...@elte.hu>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
---
kernel/smp.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN kernel/smp.c~kernel-smpc-use-=-for-csd_lock kernel/smp.c
--- a/kernel/smp.c~kernel-smpc-use-=-for-csd_lock
+++ a/kernel/smp.c
@@ -110,7 +110,7 @@ static void csd_lock_wait(struct call_si
static void csd_lock(struct call_single_data *data)
{
csd_lock_wait(data);
- data->flags = CSD_FLAG_LOCK;
+ data->flags |= CSD_FLAG_LOCK;
/*
* prevent CPU from reordering the above assignment
_
--
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