Hi Paul,

After merging the rcu tree, today's linux-next build (arm
multi_v7_defconfig) failed like this:

kernel/sched/core.c: In function 'do_task_dead':
kernel/sched/core.c:3385:2: error: implicit declaration of function 
'smp_mb__before_spinlock' [-Werror=implicit-function-declaration]
cc1: some warnings being treated as errors

Caused by commit

  4a6fc6107e90 ("sched: Replace spin_unlock_wait() with lock/unlock pair")

Interacting with commit

  a9668cd6ee28 ("locking: Remove smp_mb__before_spinlock()")

from the tip tree.

I applied this patch for now, but I assume something better is required.

From: Stephen Rothwell <s...@canb.auug.org.au>
Date: Fri, 11 Aug 2017 14:32:10 +1000
Subject: [PATCH] sched: temporary hack for locking: Remove 

Signed-off-by: Stephen Rothwell <s...@canb.auug.org.au>
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2bd00feaea15..a4f4ba2e3be6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3382,7 +3382,7 @@ void __noreturn do_task_dead(void)
         * To avoid it, we have to wait for releasing tsk->pi_lock which
         * is held by try_to_wake_up()
-       smp_mb__before_spinlock();
+       smp_mb();
Stephen Rothwell

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