linux-kernel - [PATCH RFC] vm: Adjust ifdef for TINY

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Message-ID: <20130304160237.GA1430@linux.vnet.ibm.com>
Date:	Mon, 4 Mar 2013 08:02:37 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	andi@...stfloor.org, akpm@...ux-foundation.org, mel@....ul.ie,
	daniel.vetter@...ll.ch, paul.gortmaker@...driver.com
Subject: [PATCH RFC] vm: Adjust ifdef for TINY_RCU

There is an ifdef in page_cache_get_speculative() that checks for !SMP
and TREE_RCU, which has been an impossible combination since the advent
of TINY_RCU.  The ifdef enables a fastpath that is valid when preemption
is disabled by rcu_read_lock() in UP systems, which is the case when
TINY_RCU is enabled.  This commit therefore adjusts the ifdef to generate
the fastpath when TINY_RCU is enabled.

Reported-by: Andi Kleen <andi@...stfloor.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 0e38e13..e3dea75 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -149,7 +149,7 @@ static inline int page_cache_get_speculative(struct page *page)
 {
 	VM_BUG_ON(in_interrupt());

-#if !defined(CONFIG_SMP) && defined(CONFIG_TREE_RCU)
+#ifdef CONFIG_TINY_RCU
 # ifdef CONFIG_PREEMPT_COUNT
 	VM_BUG_ON(!in_atomic());
 # endif

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