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54561073e7
Commit https://github.com/torvalds/linux/commit/94a9717b updated the rwsem's owner field to contain additional flags describing the rwsem's state. Rather then update the wrappers to mask out these bits, the code no longer relies on the owner stored by the kernel. This does increase the size of a krwlock_t but it makes the implementation less sensitive to future kernel changes. Reviewed-by: Tony Hutter <hutter2@llnl.gov> Reviewed-by: Tomohiro Kusumi <kusumi.tomohiro@gmail.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #9029
130 lines
3.8 KiB
C
130 lines
3.8 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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* Solaris Porting Layer (SPL) Reader/Writer Lock Implementation.
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*/
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#include <sys/rwlock.h>
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#include <linux/module.h>
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#if defined(CONFIG_PREEMPT_RT_FULL)
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#include <linux/rtmutex.h>
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#define RT_MUTEX_OWNER_MASKALL 1UL
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static int
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__rwsem_tryupgrade(struct rw_semaphore *rwsem)
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{
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#if defined(READER_BIAS) && defined(WRITER_BIAS)
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/*
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* After the 4.9.20-rt16 kernel the realtime patch series lifted the
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* single reader restriction. While this could be accommodated by
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* adding additional compatibility code assume the rwsem can never
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* be upgraded. All caller must already cleanly handle this case.
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*/
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return (0);
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#else
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ASSERT((struct task_struct *)
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((unsigned long)rwsem->lock.owner & ~RT_MUTEX_OWNER_MASKALL) ==
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current);
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/*
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* Prior to 4.9.20-rt16 kernel the realtime patch series, rwsem is
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* implemented as a single mutex held by readers and writers alike.
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* However, this implementation would prevent a thread from taking
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* a read lock twice, as the mutex would already be locked on
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* the second attempt. Therefore the implementation allows a
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* single thread to take a rwsem as read lock multiple times
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* tracking that nesting as read_depth counter.
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*/
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if (rwsem->read_depth <= 1) {
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/*
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* In case, the current thread has not taken the lock
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* more than once as read lock, we can allow an
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* upgrade to a write lock. rwsem_rt.h implements
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* write locks as read_depth == 0.
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*/
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rwsem->read_depth = 0;
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return (1);
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}
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return (0);
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#endif
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}
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#elif defined(CONFIG_RWSEM_GENERIC_SPINLOCK)
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static int
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__rwsem_tryupgrade(struct rw_semaphore *rwsem)
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{
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int ret = 0;
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unsigned long flags;
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spl_rwsem_lock_irqsave(&rwsem->wait_lock, flags);
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if (RWSEM_COUNT(rwsem) == SPL_RWSEM_SINGLE_READER_VALUE &&
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list_empty(&rwsem->wait_list)) {
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ret = 1;
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RWSEM_COUNT(rwsem) = SPL_RWSEM_SINGLE_WRITER_VALUE;
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}
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spl_rwsem_unlock_irqrestore(&rwsem->wait_lock, flags);
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return (ret);
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}
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#elif defined(RWSEM_ACTIVE_MASK)
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#if defined(HAVE_RWSEM_ATOMIC_LONG_COUNT)
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static int
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__rwsem_tryupgrade(struct rw_semaphore *rwsem)
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{
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long val;
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val = atomic_long_cmpxchg(&rwsem->count, SPL_RWSEM_SINGLE_READER_VALUE,
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SPL_RWSEM_SINGLE_WRITER_VALUE);
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return (val == SPL_RWSEM_SINGLE_READER_VALUE);
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}
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#else
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static int
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__rwsem_tryupgrade(struct rw_semaphore *rwsem)
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{
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typeof(rwsem->count) val;
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val = cmpxchg(&rwsem->count, SPL_RWSEM_SINGLE_READER_VALUE,
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SPL_RWSEM_SINGLE_WRITER_VALUE);
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return (val == SPL_RWSEM_SINGLE_READER_VALUE);
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}
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#endif
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#else
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static int
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__rwsem_tryupgrade(struct rw_semaphore *rwsem)
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{
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return (0);
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}
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#endif
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int
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rwsem_tryupgrade(struct rw_semaphore *rwsem)
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{
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if (__rwsem_tryupgrade(rwsem)) {
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rwsem_release(&rwsem->dep_map, 1, _RET_IP_);
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rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_);
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return (1);
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}
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return (0);
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}
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EXPORT_SYMBOL(rwsem_tryupgrade);
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int spl_rw_init(void) { return 0; }
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void spl_rw_fini(void) { }
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