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

[Noam Camus <noamc@ezchip.com>]

From: Noam Camus <noamc@ezchip.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@ezchip.com>
Cc: Peter Zijlstra <peterz@infradead.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));
 	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
-- 
1.7.1