在 2013-04-23二的 15:40 -0700，Andrew Morton写道：
> 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 ;)
That's fine, Thanks!
>
>
> 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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