linux-kernel - [PATCH 08/11] ARC: xchg: !LLSC: remove UP micro-optimization/hack

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Message-Id: <20210804191554.1252776-9-vgupta@synopsys.com>
Date:   Wed,  4 Aug 2021 12:15:51 -0700
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     linux-snps-arc@...ts.infradead.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Vladimir Isaev <Vladimir.Isaev@...opsys.com>,
        Vineet Gupta <Vineet.Gupta1@...opsys.com>
Subject: [PATCH 08/11] ARC: xchg: !LLSC: remove UP micro-optimization/hack

It gets in the way of cleaning things up and is a maintenance
pain-in-neck !

Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
---
 arch/arc/include/asm/cmpxchg.h | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
index d42917e803e1..bac9b564a140 100644
--- a/arch/arc/include/asm/cmpxchg.h
+++ b/arch/arc/include/asm/cmpxchg.h
@@ -113,15 +113,9 @@ static inline unsigned long __xchg(unsigned long val, volatile void *ptr,
  *  - For !LLSC, cmpxchg() needs to use that lock (see above) and there is lot
  *    of  kernel code which calls xchg()/cmpxchg() on same data (see llist.h)
  *    Hence xchg() needs to follow same locking rules.
- *
- * Technically the lock is also needed for UP (boils down to irq save/restore)
- * but we can cheat a bit since cmpxchg() atomic_ops_lock() would cause irqs to
- * be disabled thus can't possibly be interrupted/preempted/clobbered by xchg()
- * Other way around, xchg is one instruction anyways, so can't be interrupted
- * as such
  */
 
-#if !defined(CONFIG_ARC_HAS_LLSC) && defined(CONFIG_SMP)
+#ifndef CONFIG_ARC_HAS_LLSC
 
 #define arch_xchg(ptr, with)		\
 ({					\
@@ -134,10 +128,6 @@ static inline unsigned long __xchg(unsigned long val, volatile void *ptr,
 	old_val;			\
 })
 
-#else
-
-#define arch_xchg(ptr, with)  _xchg(ptr, with)
-
 #endif
 
 /*
-- 
2.25.1