From: Milton Miller <miltonm@bga.com>
Date: Tue, 15 Mar 2011 19:27:16 +0000 (-0600)
Subject: call_function_many: fix list delete vs add race
X-Git-Tag: v2.6.37.5~12
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9bc79b33d6e75d2b2760efb39a40e36de0587cdd;p=pandora-kernel.git

call_function_many: fix list delete vs add race

commit e6cd1e07a185d5f9b0aa75e020df02d3c1c44940 upstream.

Peter pointed out there was nothing preventing the list_del_rcu in
smp_call_function_interrupt from running before the list_add_rcu in
smp_call_function_many.

Fix this by not setting refs until we have gotten the lock for the list.
Take advantage of the wmb in list_add_rcu to save an explicit additional
one.

I tried to force this race with a udelay before the lock & list_add and
by mixing all 64 online cpus with just 3 random cpus in the mask, but
was unsuccessful.  Still, inspection shows a valid race, and the fix is
a extension of the existing protection window in the current code.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---

Reading git-diff-tree failed