linux-kernel - Re: [tip:locking/core] rwsem: Support optimistic spinning

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Date:	Mon, 19 May 2014 14:47:36 -0700
From:	Davidlohr Bueso <davidlohr@...com>
To:	mingo@...nel.org, torvalds@...ux-foundation.org,
	peterz@...radead.org, peter@...leysoftware.com, jason.low2@...com,
	alex.shi@...aro.org, riel@...hat.com, akpm@...ux-foundation.org,
	aarcange@...hat.com, tglx@...utronix.de, scott.norton@...com,
	linux-kernel@...r.kernel.org, hpa@...or.com, andi@...stfloor.org,
	tim.c.chen@...ux.intel.com, paulmck@...ux.vnet.ibm.com,
	walken@...gle.com, aswin@...com
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:locking/core] rwsem: Support optimistic spinning

Andrew had put this patch in -next for a while, and Stephen Rothwell was
able to trigger some warnings: https://lkml.org/lkml/2014/5/19/627

8<----------------------------------------------------------------
From: Davidlohr Bueso <davidlohr@...com>
Subject: [PATCH] rwsem: Fix warnings for CONFIG_RWSEM_GENERIC_SPINLOCK

Optimistic spinning is only used by the xadd variant
of rw-semaphores. Make sure that we use the old version
of the __RWSEM_INITIALIZER macro for systems that rely
on the spinlock one, otherwise warnings can be triggered,
such as the following reported on an arm box:

ipc/ipcns_notifier.c:22:8: warning: excess elements in struct initializer [enabled by default]
ipc/ipcns_notifier.c:22:8: warning: (near initialization for 'ipcns_chain.rwsem') [enabled by default]
ipc/ipcns_notifier.c:22:8: warning: excess elements in struct initializer [enabled by default]
ipc/ipcns_notifier.c:22:8: warning: (near initialization for 'ipcns_chain.rwsem') [enabled by default]

Signed-off-by: Davidlohr Bueso <davidlohr@...com>
---
 include/linux/rwsem.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index 3e108f1..091d993 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -64,7 +64,7 @@ static inline int rwsem_is_locked(struct rw_semaphore *sem)
 # define __RWSEM_DEP_MAP_INIT(lockname)
 #endif
 
-#ifdef CONFIG_SMP
+#if defined(CONFIG_SMP) && defined(CONFIG_RWSEM_XCHGADD_ALGORITHM)
 #define __RWSEM_INITIALIZER(name)			\
 	{ RWSEM_UNLOCKED_VALUE,				\
 	  __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock),	\
-- 
1.8.1.4



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