On Sun, Jan 25, 2015 at 11:36:05PM -0800, Davidlohr Bueso wrote: > The need for the smp_mb in __rwsem_do_wake should be > properly documented. Applies to both xadd and spinlock > variants. > > Signed-off-by: Davidlohr Bueso <dbu...@suse.de> > --- > kernel/locking/rwsem-spinlock.c | 5 +++++ > kernel/locking/rwsem-xadd.c | 5 +++++ > 2 files changed, 10 insertions(+) > > diff --git a/kernel/locking/rwsem-spinlock.c b/kernel/locking/rwsem-spinlock.c > index 2555ae1..54f7a17 100644 > --- a/kernel/locking/rwsem-spinlock.c > +++ b/kernel/locking/rwsem-spinlock.c > @@ -85,6 +85,11 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wakewrite) > > list_del(&waiter->list); > tsk = waiter->task; > + /* > + * Ensure that all cores see the read before > + * setting it to the waiter task to nil, as that > + * grants the read lock to the next task. > + */ > smp_mb(); > waiter->task = NULL; > wake_up_process(tsk);
Could you enhance that comment by pointing at the pairing code? Is that the wait loop in rwsem_down_read_failed()? Also, the comment confuses, how can all cores observe a read into a local variable? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
