Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: [PATCH] markers: bit-field is not thread-safe nor smp-safe | Date | Fri, 10 Oct 2008 13:26:36 +0900 (JST) |
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Hi Lai-san,
> > bit-field is not thread-safe nor smp-safe. > > struct marker_entry.rcu_pending is not protected by any lock > in rcu-callback free_old_closure(). > so we must turn it into a safe type.
hmmm however, char also doesn't smp-safe because some architecture doesn't have any byte load/store instruction.
It seems bogus solution to me ;)
> detail: > > I suppose rcu_pending and ptype are store in struct marker_entry.tmp1 > > free_old_closure() side: change ptype side: > > | load struct marker_entry.tmp1 > --------------------------------|-------------------------------- > | change ptype bit in tmp1 > load struct marker_entry.tmp1 | > change rcu_pending bit in tmp1 | > store tmp1 | > --------------------------------|-------------------------------- > | store tmp1 > > now this result equals that free_old_closure() do not change rcu_pending bit, bug. > > see also: http://en.wikipedia.org/wiki/Bit_field > > Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> > --- > diff --git a/kernel/marker.c b/kernel/marker.c > index 7d1faec..4777218 100644 > --- a/kernel/marker.c > +++ b/kernel/marker.c > @@ -62,7 +62,7 @@ struct marker_entry { > int refcount; /* Number of times armed. 0 if disarmed. */ > struct rcu_head rcu; > void *oldptr; > - unsigned char rcu_pending:1; > + unsigned char rcu_pending; > unsigned char ptype:1; > char name[0]; /* Contains name'\0'format'\0' */ > };
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