Re: [PATCH 4.14 29/72] locking/qspinlock, x86: Provide liveness guarantee

[Sudip Mukherjee <sudipm.mukherjee@gmail.com>]

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On Thu, Dec 20, 2018 at 04:40:30PM +0100, Greg Kroah-Hartman wrote:
> On Thu, Dec 20, 2018 at 12:14:00PM +0000, Sudip Mukherjee wrote:
> > Hi Greg,
> > 
> > On Thu, Dec 20, 2018 at 9:28 AM Greg Kroah-Hartman
> > <gregkh@linuxfoundation.org> wrote:
> > >
> > > 4.14-stable review patch.  If anyone has any objections, please let me know.
> > >
> > > ------------------
> > >
> > > commit 7aa54be2976550f17c11a1c3e3630002dea39303 upstream.
> > 
> > Another upstream commit fixes this.
> > b987ffc18fb3 ("x86/qspinlock: Fix compile error")
> 
> Maybe, but that commit doesn't apply to any of these stable trees :(
> 
> Care to provide a backport?

Attached now.

--
Regards
Sudip

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From 35c4feb16f5204faa40e9b0451cd86549819f375 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Fri, 2 Nov 2018 14:26:53 +0100
Subject: [PATCH] x86/qspinlock: Fix compile error

commit b987ffc18fb3b3b76b059aa9e372dbee26f7c4f2 upstream

With a compiler that has asm-goto but not asm-cc-output and
CONFIG_PROFILE_ALL_BRANCHES=y we get a compiler error:

  arch/x86/include/asm/rmwcc.h:23:17: error: jump into statement expression

Fix this by writing the if() as a boolean multiplication instead.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-kernel@vger.kernel.org
Fixes: 7aa54be29765 ("locking/qspinlock, x86: Provide liveness guarantee")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
---
 arch/x86/include/asm/qspinlock.h | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h
index f784b95e44df..f0f2dd74b8c9 100644
--- a/arch/x86/include/asm/qspinlock.h
+++ b/arch/x86/include/asm/qspinlock.h
@@ -19,10 +19,14 @@ static __always_inline bool __queued_RMW_btsl(struct qspinlock *lock)
 
 static __always_inline u32 queued_fetch_set_pending_acquire(struct qspinlock *lock)
 {
-	u32 val = 0;
+	u32 val;
 
-	if (__queued_RMW_btsl(lock))
-		val |= _Q_PENDING_VAL;
+	/*
+	 * We can't use GEN_BINARY_RMWcc() inside an if() stmt because asm goto
+	 * and CONFIG_PROFILE_ALL_BRANCHES=y results in a label inside a
+	 * statement expression, which GCC doesn't like.
+	 */
+	val = __queued_RMW_btsl(lock) * _Q_PENDING_VAL;
 
 	val |= atomic_read(&lock->val) & ~_Q_PENDING_MASK;
 
-- 
2.11.0