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The main complication from the RT patch set is that the RW semaphore locks change such that read locks on an rwsem can be taken only by a single thread. All other threads are locked out. This single thread can take a read lock multiple times though. The underlying implementation changes to a mutex with an additional read_depth count. The implementation can be best understood by inspecting the RT patch. rwsem_rt.h and rt.c give the best insight into how RT rwsem works. My implementation for rwsem_tryupgrade is basically an inversion of rt_downgrade_write found in rt.c. Please see the comments in the code. Unfortunately, I have to drop SPLAT rwlock test4 completely as this test tries to take multiple locks from different threads, which RT rwsems do not support. Otherwise SPLAT, zconfig.sh, zpios-sanity.sh and zfs-tests.sh pass on my Debian-testing VM with the kernel linux-image-4.8.0-1-rt-amd64. Tested-by: kernelOfTruth <kerneloftruth@gmail.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Clemens Fruhwirth <clemens@endorphin.org> Closes zfsonlinux/zfs#5491 Closes #589 Closes #308
68 lines
2.7 KiB
C
68 lines
2.7 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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#if defined(CONFIG_PREEMPT_RT_FULL)
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#define SPL_RWSEM_SINGLE_READER_VALUE (1)
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#define SPL_RWSEM_SINGLE_WRITER_VALUE (0)
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#elif defined(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 changed activity to count for rwsem-spinlock */
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#if defined(CONFIG_PREEMPT_RT_FULL)
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#define RWSEM_COUNT(sem) sem->read_depth
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#elif defined(HAVE_RWSEM_ACTIVITY)
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#define RWSEM_COUNT(sem) sem->activity
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/* Linux 4.8 changed count to an atomic_long_t for !rwsem-spinlock */
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#elif defined(HAVE_RWSEM_ATOMIC_LONG_COUNT)
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#define RWSEM_COUNT(sem) atomic_long_read(&(sem)->count)
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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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