linux-kernel - [GIT pull] locking/urgent for 5.7-rc5

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Date:   Sun, 10 May 2020 11:55:57 -0000
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org
Subject: [GIT pull] locking/urgent for 5.7-rc5

Linus,

please pull the latest locking/urgent branch from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git locking-urgent-2020-05-10

up to:  8101b5a1531f: ARM: futex: Address build warning


A single fix for the fallout of the recent futex uacess rework.

With those changes GCC9 fails to analyze arch_futex_atomic_op_inuser()
correctly and emits a 'maybe unitialized' warning. While we usually ignore
compiler stupidity the conditional store is pointless anyway because the
correct case has to store. For the fault case the extra store does no harm.

Thanks,

	tglx

------------------>
Thomas Gleixner (1):
      ARM: futex: Address build warning


 arch/arm/include/asm/futex.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/futex.h b/arch/arm/include/asm/futex.h
index e133da303a98..a9151884bc85 100644
--- a/arch/arm/include/asm/futex.h
+++ b/arch/arm/include/asm/futex.h
@@ -165,8 +165,13 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
 	preempt_enable();
 #endif
 
-	if (!ret)
-		*oval = oldval;
+	/*
+	 * Store unconditionally. If ret != 0 the extra store is the least
+	 * of the worries but GCC cannot figure out that __futex_atomic_op()
+	 * is either setting ret to -EFAULT or storing the old value in
+	 * oldval which results in a uninitialized warning at the call site.
+	 */
+	*oval = oldval;
 
 	return ret;
 }