Date: Thu, 10 Aug 2006 09:11:29 -0700
From: "Paul E. McKenney" <paulmck@us.ibm.com>
To: Stelian Pop <stelian@popies.net>
Cc: Mike Christie <michaelc@cs.wisc.edu>, linux-kernel@vger.kernel.org,
       akpm@osdl.org, paulus@au1.ibm.com, anton@au1.ibm.com,
       open-iscsi@googlegroups.com, pradeep@us.ibm.com, mashirle@us.ibm.com
Subject: Re: [PATCH] memory ordering in __kfifo primitives
Message-ID: <20060810161129.GF1298@us.ibm.com>
Reply-To: paulmck@us.ibm.com
References: <20060810001823.GA3026@us.ibm.com> <20060810003310.GA3071@us.ibm.com> <44DAC892.7000100@cs.wisc.edu> <20060810134135.GB1298@us.ibm.com> <1155220013.1108.4.camel@localhost.localdomain> <20060810153915.GE1298@us.ibm.com> <1155224842.5393.13.camel@localhost.localdomain>
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On Thu, Aug 10, 2006 at 05:47:22PM +0200, Stelian Pop wrote:
> Le jeudi 10 ao?t 2006 ? 08:39 -0700, Paul E. McKenney a ?crit :
> > On Thu, Aug 10, 2006 at 04:26:53PM +0200, Stelian Pop wrote:
> > > Le jeudi 10 ao?t 2006 ? 06:41 -0700, Paul E. McKenney a ?crit :
> > > 
> > > > 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
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