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f58040c0fc
Current rw_tryupgrade does rw_exit and then rw_tryenter(RW_RWITER), and then does rw_enter(RW_READER) if it fails. This violate the assumption that rw_tryupgrade should be atomic and could cause extra contention or even lock inversion. This patch we implement a proper rw_tryupgrade. For rwsem-spinlock, we take the spinlock to check rwsem->count and rwsem->wait_list. For normal rwsem, we use cmpxchg on rwsem->count to change the value from single reader to single writer. Signed-off-by: Chunwei Chen <david.chen@osnexus.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Tim Chase <tim@chase2k.com> Closes zfsonlinux/zfs#4692 Closes #554
60 lines
2.4 KiB
C
60 lines
2.4 KiB
C
/*****************************************************************************\
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* Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC.
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* Copyright (C) 2007 The Regents of the University of California.
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* Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
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* Written by Brian Behlendorf <behlendorf1@llnl.gov>.
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* UCRL-CODE-235197
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*
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* This file is part of the SPL, Solaris Porting Layer.
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* For details, see <http://zfsonlinux.org/>.
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*
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* The SPL is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by the
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* Free Software Foundation; either version 2 of the License, or (at your
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* option) any later version.
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*
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* The SPL is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with the SPL. If not, see <http://www.gnu.org/licenses/>.
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\*****************************************************************************/
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#ifndef _SPL_RWSEM_COMPAT_H
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#define _SPL_RWSEM_COMPAT_H
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#include <linux/rwsem.h>
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#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
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#define SPL_RWSEM_SINGLE_READER_VALUE (1)
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#define SPL_RWSEM_SINGLE_WRITER_VALUE (-1)
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#else
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#define SPL_RWSEM_SINGLE_READER_VALUE (RWSEM_ACTIVE_READ_BIAS)
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#define SPL_RWSEM_SINGLE_WRITER_VALUE (RWSEM_ACTIVE_WRITE_BIAS)
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#endif
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/* Linux 3.16 change activity to count for rwsem-spinlock */
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#ifdef HAVE_RWSEM_ACTIVITY
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#define RWSEM_COUNT(sem) sem->activity
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#else
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#define RWSEM_COUNT(sem) sem->count
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#endif
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int rwsem_tryupgrade(struct rw_semaphore *rwsem);
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#if defined(RWSEM_SPINLOCK_IS_RAW)
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#define spl_rwsem_lock_irqsave(lk, fl) raw_spin_lock_irqsave(lk, fl)
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#define spl_rwsem_unlock_irqrestore(lk, fl) raw_spin_unlock_irqrestore(lk, fl)
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#define spl_rwsem_trylock_irqsave(lk, fl) raw_spin_trylock_irqsave(lk, fl)
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#else
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#define spl_rwsem_lock_irqsave(lk, fl) spin_lock_irqsave(lk, fl)
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#define spl_rwsem_unlock_irqrestore(lk, fl) spin_unlock_irqrestore(lk, fl)
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#define spl_rwsem_trylock_irqsave(lk, fl) spin_trylock_irqsave(lk, fl)
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#endif /* RWSEM_SPINLOCK_IS_RAW */
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#define spl_rwsem_is_locked(rwsem) rwsem_is_locked(rwsem)
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#endif /* _SPL_RWSEM_COMPAT_H */
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