netdev - [patch] ipvs: force read of atomic

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Date:	Wed, 8 Aug 2007 11:33:00 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Wensong Zhang <wensong@...ux-vs.org>,
	Simon Horman <horms@...ge.net.au>
Subject: [patch] ipvs: force read of atomic_t in while loop

From: Heiko Carstens <heiko.carstens@...ibm.com>

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 <wensong@...ux-vs.org>
Cc: Simon Horman <horms@...ge.net.au>
Cc: David Miller <davem@...emloft.net>
Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
---

Just saw this while grepping for atomic_reads in a while loops.
Maybe we should re-add the volatile to atomic_t. Not sure.

 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);
-
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