Re: [PATCH] memory ordering in __kfifo primitives

["Paul E. McKenney" <paulmck@us.ibm.com>]

On Thu, Aug 10, 2006 at 05:47:22PM +0200, Stelian Pop wrote:
> Le jeudi 10 août 2006 à 08:39 -0700, Paul E. McKenney a écrit :
> > On Thu, Aug 10, 2006 at 04:26:53PM +0200, Stelian Pop wrote:
> > > Le jeudi 10 août 2006 à 06:41 -0700, Paul E. McKenney a écrit :
> > > 
> > > > I am happy to go either way -- the patch with the memory barriers
> > > > (which does have the side-effect of slowing down kfifo_get() and
> > > > kfifo_put(), by the way), or a patch removing the comments saying
> > > > that it is OK to invoke __kfifo_get() and __kfifo_put() without
> > > > locking.
> > > > 
> > > > Any other thoughts on which is better?  (1) the memory barriers or
> > > > (2) requiring the caller hold appropriate locks across calls to
> > > > __kfifo_get() and __kfifo_put()?
> > > 
> > > If someone wants to use explicit locking, he/she can go with kfifo_get()
> > > instead of the __ version.
> > 
> > However, the kfifo_get()/kfifo_put() interfaces use the internal lock,
> 
> ... and the internal lock can be supplied by the user at kfifo_alloc()
> time.

Would that really work for them?  Looks to me like it would result
in self-deadlock if they passed in session->lock.

Or did you have something else in mind for them?

These are the __kfifo_get() and __kfifo_put() uses in:

	drivers/scsi/iscsi_tcp.c
	drivers/scsi/libiscsi.c
	drivers/infiniband/ulp/iser/iser_initiator.c

							Thanx, Paul