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d503b971f4
The spl_rwsem_is_locked() compatibility function has been observed to be a hot spot. The root cause of this is that we must check the rwsem activity under the rwsem->wait_lock to avoid a race. When the lock is busy significant contention can occur. The upstream kernel fix for this race had the insight that by using spin_trylock_irqsave() this contention could be avoided. When the lock is contended it's reasonable to return that it is locked. This change updates the SPLs implemention to be like the upstream kernel. Since the kernel code has been in use for years now this a low risk change. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
67 lines
2.6 KiB
C
67 lines
2.6 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://github.com/behlendorf/spl/>.
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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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#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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/*
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* Prior to Linux 2.6.33 there existed a race condition in rwsem_is_locked().
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* The semaphore's activity was checked outside of the wait_lock which
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* could result in some readers getting the incorrect activity value.
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*
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* When a kernel without this fix is detected the SPL takes responsibility
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* for acquiring the wait_lock to avoid this race.
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*/
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#if defined(RWSEM_IS_LOCKED_TAKES_WAIT_LOCK)
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#define spl_rwsem_is_locked(rwsem) rwsem_is_locked(rwsem)
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#else
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static inline int
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spl_rwsem_is_locked(struct rw_semaphore *rwsem)
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{
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unsigned long flags;
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int rc = 1;
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if (spl_rwsem_trylock_irqsave(&rwsem->wait_lock, flags)) {
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rc = rwsem_is_locked(rwsem);
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spl_rwsem_unlock_irqrestore(&rwsem->wait_lock, flags);
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}
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return (rc);
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}
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#endif /* RWSEM_IS_LOCKED_TAKES_WAIT_LOCK */
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#endif /* _SPL_RWSEM_COMPAT_H */
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