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78e05b1421
Similar to the previous commit which described why we need to add a barrier to arch_spin_is_locked(), we have a similar problem with spin_unlock_wait(). We need a barrier on entry to ensure any spinlock we have previously taken is visibly locked prior to the load of lock->slock. It's also not clear if spin_unlock_wait() is intended to have ACQUIRE semantics. For now be conservative and add a barrier on exit to give it ACQUIRE semantics. Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
85 lines
2.2 KiB
C
85 lines
2.2 KiB
C
/*
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* Spin and read/write lock operations.
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*
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* Copyright (C) 2001-2004 Paul Mackerras <paulus@au.ibm.com>, IBM
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* Copyright (C) 2001 Anton Blanchard <anton@au.ibm.com>, IBM
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* Copyright (C) 2002 Dave Engebretsen <engebret@us.ibm.com>, IBM
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* Rework to support virtual processors
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#include <linux/kernel.h>
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#include <linux/spinlock.h>
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#include <linux/export.h>
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#include <linux/stringify.h>
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#include <linux/smp.h>
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/* waiting for a spinlock... */
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#if defined(CONFIG_PPC_SPLPAR)
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#include <asm/hvcall.h>
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#include <asm/smp.h>
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void __spin_yield(arch_spinlock_t *lock)
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{
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unsigned int lock_value, holder_cpu, yield_count;
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lock_value = lock->slock;
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if (lock_value == 0)
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return;
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holder_cpu = lock_value & 0xffff;
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BUG_ON(holder_cpu >= NR_CPUS);
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yield_count = be32_to_cpu(lppaca_of(holder_cpu).yield_count);
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if ((yield_count & 1) == 0)
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return; /* virtual cpu is currently running */
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rmb();
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if (lock->slock != lock_value)
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return; /* something has changed */
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plpar_hcall_norets(H_CONFER,
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get_hard_smp_processor_id(holder_cpu), yield_count);
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}
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/*
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* Waiting for a read lock or a write lock on a rwlock...
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* This turns out to be the same for read and write locks, since
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* we only know the holder if it is write-locked.
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*/
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void __rw_yield(arch_rwlock_t *rw)
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{
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int lock_value;
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unsigned int holder_cpu, yield_count;
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lock_value = rw->lock;
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if (lock_value >= 0)
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return; /* no write lock at present */
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holder_cpu = lock_value & 0xffff;
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BUG_ON(holder_cpu >= NR_CPUS);
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yield_count = be32_to_cpu(lppaca_of(holder_cpu).yield_count);
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if ((yield_count & 1) == 0)
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return; /* virtual cpu is currently running */
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rmb();
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if (rw->lock != lock_value)
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return; /* something has changed */
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plpar_hcall_norets(H_CONFER,
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get_hard_smp_processor_id(holder_cpu), yield_count);
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}
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#endif
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void arch_spin_unlock_wait(arch_spinlock_t *lock)
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{
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smp_mb();
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while (lock->slock) {
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HMT_low();
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if (SHARED_PROCESSOR)
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__spin_yield(lock);
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}
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HMT_medium();
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smp_mb();
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}
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EXPORT_SYMBOL(arch_spin_unlock_wait);
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