[CRIU] [PATCH 5/5] x86: atomic -- Adopt code from linux kernel

[Cyrill Gorcunov]

On Fri, Feb 15, 2013 at 05:28:42PM +0400, Pavel Emelyanov wrote:
> On 02/06/2013 12:04 AM, Cyrill Gorcunov wrote:
> > 
> > This allow us to eliminate "asm/types.h" inclusion as well,
> > together with simplifying the code.
> > 
> > Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
> > ---
> >  arch/x86/include/asm/atomic.h | 92 +++++++++++++++++++------------------------
> >  include/lock.h                |  3 +-
> >  2 files changed, 43 insertions(+), 52 deletions(-)
> > 
> 
> 
> > @@ -119,7 +119,8 @@ static void inline mutex_lock(mutex_t *m)
> >  	u32 c;
> >  	int ret;
> >  
> > -	while ((c = atomic_inc(&m->raw))) {
> > +	while ((c = atomic_read(&m->raw))) {
> > +		atomic_inc(&m->raw);
> 
> This is not equal change. It was while (atomic_get_and_inc) now its while (atomic_get) atomic_inc.

Which actually doesn't change much. Look, atomic_inc was incrementing value and
returning its previous meaning, now we do the same but this looks as "two"
operations from C code, but the cycle below is constructed to be lockless so you will
not get any harm in such transition. I rather feel sorry that I wrote it in
"lock xchg" manner earlier.