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Date: Mon, 27 Nov 2017 14:05:25 +0100 (CET)
From: Sebastian Ott <sebott@linux.vnet.ibm.com>
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To: Will Deacon <will.deacon@arm.com>
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        Martin Schwidefsky <schwidefsky@de.ibm.com>,
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        linux-kernel@vger.kernel.org
Subject: Re: [bisected] system hang after boot
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On Mon, 27 Nov 2017, Will Deacon wrote:
> Sebastian: could you try the diff below, please? If that fixes s390, then
> we can debate the merits of GENERIC_LOCKBREAK independently of fixing this
> issue.
> 
> Thanks,
> 
> Will
> 
> --->8
> 
> diff --git a/kernel/locking/spinlock.c b/kernel/locking/spinlock.c
> index 1fd1a7543cdd..0ebb253e2199 100644
> --- a/kernel/locking/spinlock.c
> +++ b/kernel/locking/spinlock.c
> @@ -68,8 +68,8 @@ void __lockfunc __raw_##op##_lock(locktype##_t *lock)			\
>  									\
>  		if (!(lock)->break_lock)				\
>  			(lock)->break_lock = 1;				\
> -		while ((lock)->break_lock)				\
> -			arch_##op##_relax(&lock->raw_lock);		\
> +									\
> +		arch_##op##_relax(&lock->raw_lock);			\
>  	}								\
>  	(lock)->break_lock = 0;						\
>  }									\
> @@ -88,8 +88,8 @@ unsigned long __lockfunc __raw_##op##_lock_irqsave(locktype##_t *lock)	\
>  									\
>  		if (!(lock)->break_lock)				\
>  			(lock)->break_lock = 1;				\
> -		while ((lock)->break_lock)				\
> -			arch_##op##_relax(&lock->raw_lock);		\
> +									\
> +		arch_##op##_relax(&lock->raw_lock);			\
>  	}								\
>  	(lock)->break_lock = 0;						\
>  	return flags;							\

I tested that on top of 4.15.0-rc1 and it worked!

Sebastian