From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Date: Tue, 14 Sep 2010 00:24:21 +0000 (-0700)
Subject: rcu: only one evaluation of arg in rcu_dereference_check() unless sparse
X-Git-Tag: v2.6.37-rc1~215^2~9
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=53ecfba259f54b6967a35d19f4a564e3bc07997f;p=pandora-kernel.git

rcu: only one evaluation of arg in rcu_dereference_check() unless sparse

The current version of the __rcu_access_pointer(), __rcu_dereference_check(),
and __rcu_dereference_protected() macros evaluate their "p" argument
three times, not counting typeof()s.  This is bad news if that argument
contains a side effect.  This commit therefore evaluates this argument
only once in normal kernel builds.  However, the straightforward approach
defeats sparse's RCU-pointer checking, so when __CHECKER__ is defined,
the additional pair of evaluations of the "p" argument are performed in
order to permit sparse to detect misuse of RCU-protected pointers.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
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