linux-kernel - Re: [PATCH v1 05/20] ARC: rwlock: disable interrupts in !LLSC variant

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Message-ID: <56373019.6080501@synopsys.com>
Date:	Mon, 2 Nov 2015 15:12:49 +0530
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	Noam Camus <noamc@...hip.com>, <linux-snps-arc@...ts.infradead.org>
CC:	<linux-kernel@...r.kernel.org>, <talz@...hip.com>,
	<gilf@...hip.com>, <cmetcalf@...hip.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v1 05/20] ARC: rwlock: disable interrupts in !LLSC variant

On Saturday 31 October 2015 06:45 PM, Noam Camus wrote:
> From: Noam Camus <noamc@...hip.com>
> 
> If we hold rw->lock_mutex and interrupt occures we may
> end up spinning on it for ever during softirq.
> 
> Below you may see an example for interrupt we get while
> nl_table_lock is holding its rw->lock_mutex and we spinned
> on it for ever.
> 
> The concept for the fix was taken from SPARC.
> 
> [2015-05-12 19:16:12] Stack Trace:
> [2015-05-12 19:16:12]   arc_unwind_core+0xb8/0x11c
> [2015-05-12 19:16:12]   dump_stack+0x68/0xac
> [2015-05-12 19:16:12]   _raw_read_lock+0xa8/0xac
> [2015-05-12 19:16:12]   netlink_broadcast_filtered+0x56/0x35c
> [2015-05-12 19:16:12]   nlmsg_notify+0x42/0xa4
> [2015-05-12 19:16:13]   neigh_update+0x1fe/0x44c
> [2015-05-12 19:16:13]   neigh_event_ns+0x40/0xa4
> [2015-05-12 19:16:13]   arp_process+0x46e/0x5a8
> [2015-05-12 19:16:13]   __netif_receive_skb_core+0x358/0x500
> [2015-05-12 19:16:13]   process_backlog+0x92/0x154
> [2015-05-12 19:16:13]   net_rx_action+0xb8/0x188
> [2015-05-12 19:16:13]   __do_softirq+0xda/0x1d8
> [2015-05-12 19:16:14]   irq_exit+0x8a/0x8c
> [2015-05-12 19:16:14]   arch_do_IRQ+0x6c/0xa8
> [2015-05-12 19:16:14]   handle_interrupt_level1+0xe4/0xf0
> 
> Signed-off-by: Noam Camus <noamc@...hip.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> ---
>  arch/arc/include/asm/spinlock.h |   14 ++++++++++++++
>  1 files changed, 14 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/arc/include/asm/spinlock.h b/arch/arc/include/asm/spinlock.h
> index db8c59d..800e7c4 100644
> --- a/arch/arc/include/asm/spinlock.h
> +++ b/arch/arc/include/asm/spinlock.h
> @@ -610,7 +610,9 @@ static inline void arch_spin_unlock(arch_spinlock_t *lock)
>  static inline int arch_read_trylock(arch_rwlock_t *rw)
>  {
>  	int ret = 0;
> +	unsigned long flags;
>  
> +	local_irq_save(flags);
>  	arch_spin_lock(&(rw->lock_mutex));
>  
>  	/*
> @@ -623,6 +625,7 @@ static inline int arch_read_trylock(arch_rwlock_t *rw)
>  	}
>  
>  	arch_spin_unlock(&(rw->lock_mutex));
> +	local_irq_restore(flags);
>  
>  	smp_mb();
>  	return ret;
> @@ -632,7 +635,9 @@ static inline int arch_read_trylock(arch_rwlock_t *rw)
>  static inline int arch_write_trylock(arch_rwlock_t *rw)
>  {
>  	int ret = 0;
> +	unsigned long flags;
>  
> +	local_irq_save(flags);
>  	arch_spin_lock(&(rw->lock_mutex));
>  
>  	/*
> @@ -646,6 +651,7 @@ static inline int arch_write_trylock(arch_rwlock_t *rw)
>  		ret = 1;
>  	}
>  	arch_spin_unlock(&(rw->lock_mutex));
> +	local_irq_restore(flags);
>  
>  	return ret;
>  }
> @@ -664,16 +670,24 @@ static inline void arch_write_lock(arch_rwlock_t *rw)
>  
>  static inline void arch_read_unlock(arch_rwlock_t *rw)
>  {
> +	unsigned long flags;
> +
> +	local_irq_save(flags);
>  	arch_spin_lock(&(rw->lock_mutex));


Isn't raw_spin_lock_irqsave() equivalent and more concise ?


>  	rw->counter++;
>  	arch_spin_unlock(&(rw->lock_mutex));
> +	local_irq_restore(flags);
>  }
>  
>  static inline void arch_write_unlock(arch_rwlock_t *rw)
>  {
> +	unsigned long flags;
> +
> +	local_irq_save(flags);
>  	arch_spin_lock(&(rw->lock_mutex));
>  	rw->counter = __ARCH_RW_LOCK_UNLOCKED__;
>  	arch_spin_unlock(&(rw->lock_mutex));
> +	local_irq_restore(flags);
>  }
>  
>  #endif
> 

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