From mboxrd@z Thu Jan 1 00:00:00 1970 From: Horms Subject: Re: [patch] ipvs: force read of atomic_t in while loop Date: Wed, 8 Aug 2007 18:45:44 +0900 Message-ID: <20070808094542.GA5901@verge.net.au> References: <20070808093300.GA14530@osiris.boeblingen.de.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andrew Morton , David Miller , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, Martin Schwidefsky , Wensong Zhang To: Heiko Carstens Return-path: Content-Disposition: inline In-Reply-To: <20070808093300.GA14530@osiris.boeblingen.de.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wed, Aug 08, 2007 at 11:33:00AM +0200, Heiko Carstens wrote: > From: Heiko Carstens > > For architectures that don't have a volatile atomic_ts constructs like > while (atomic_read(&something)); might result in endless loops since a > barrier() is missing which forces the compiler to generate code that > actually reads memory contents. > Fix this in ipvs by using the IP_VS_WAIT_WHILE macro which resolves to > while (expr) { cpu_relax(); } > (why isn't this open coded btw?) > > Cc: Wensong Zhang > Cc: Simon Horman > Cc: David Miller > Cc: Martin Schwidefsky > Signed-off-by: Heiko Carstens > --- > > Just saw this while grepping for atomic_reads in a while loops. > Maybe we should re-add the volatile to atomic_t. Not sure. This looks good to me. A little wile back I noticed a few places where IP_VS_WAIT_WHILE seemed to be curiously unused, then I got distracted... Signed-off-by: Simon Horman > > net/ipv4/ipvs/ip_vs_ctl.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > Index: linux-2.6/net/ipv4/ipvs/ip_vs_ctl.c > =================================================================== > --- linux-2.6.orig/net/ipv4/ipvs/ip_vs_ctl.c > +++ linux-2.6/net/ipv4/ipvs/ip_vs_ctl.c > @@ -909,7 +909,7 @@ ip_vs_edit_dest(struct ip_vs_service *sv > write_lock_bh(&__ip_vs_svc_lock); > > /* Wait until all other svc users go away */ > - while (atomic_read(&svc->usecnt) > 1) {}; > + IP_VS_WAIT_WHILE(atomic_read(&svc->usecnt) > 1); > > /* call the update_service, because server weight may be changed */ > svc->scheduler->update_service(svc); -- Horms H: http://www.vergenet.net/~horms/ W: http://www.valinux.co.jp/en/