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The behavior of RW_*_HELD was updated because it was not quite right. It is not sufficient to return non-zero when the lock is help, we must only do this when the current task in the holder. This means we need to track the lock owner which is not something tracked in a Linux semaphore. After some experimentation the solution I settled on was to embed the Linux semaphore at the start of a larger krwlock_t structure which includes the owner field. This maintains good performance and allows us to cleanly intergrate with the kernel lock analysis tools. My reasons: 1) By placing the Linux semaphore at the start of krwlock_t we can then simply cast krwlock_t to a rw_semaphore and pass that on to the linux kernel. This allows us to use '#defines so the preprocessor can do direct replacement of the Solaris primative with the linux equivilant. This is important because it then maintains the location information for each rw_* call point. 2) Additionally, by adding the owner to krwlock_t we can keep this needed extra information adjacent to the lock itself. This removes the need for a fancy lookup to get the owner which is optimal for performance. We can also leverage the existing spin lock in the semaphore to ensure owner is updated correctly. 3) All helper functions which do not need to strictly be implemented as a define to preserve location information can be done as a static inline function. 4) Adding the owner to krwlock_t allows us to remove all memory allocations done during lock initialization. This is good for all the obvious reasons, we do give up the ability to specific the lock name. The Linux profiling tools will stringify the lock name used in the code via the preprocessor and use that. Update rwlocks validated on: - SLES10 (ppc64) - SLES11 (x86_64) - CHAOS4.2 (x86_64) - RHEL5.3 (x86_64) - RHEL6 (x86_64) - FC11 (x86_64)
235 lines
9.0 KiB
C
235 lines
9.0 KiB
C
/*
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* This file is part of the SPL: Solaris Porting Layer.
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*
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* Copyright (c) 2009 Lawrence Livermore National Security, LLC.
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* Produced at Lawrence Livermore National Laboratory
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* Written by:
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* Brian Behlendorf <behlendorf1@llnl.gov>,
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* Herb Wartens <wartens2@llnl.gov>,
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* Jim Garlick <garlick@llnl.gov>
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* UCRL-CODE-235197
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*
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* This 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
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This 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 this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#ifndef _SPL_RWLOCK_H
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#define _SPL_RWLOCK_H
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#include <sys/types.h>
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#include <linux/rwsem.h>
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typedef enum {
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RW_DRIVER = 2,
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RW_DEFAULT = 4
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} krw_type_t;
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typedef enum {
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RW_NONE = 0,
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RW_WRITER = 1,
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RW_READER = 2
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} krw_t;
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typedef struct {
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struct rw_semaphore rw_rwlock;
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kthread_t *rw_owner;
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} krwlock_t;
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/*
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* For the generic and x86 implementations of rw-semaphores the following
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* is true. If your semaphore implementation internally represents the
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* semaphore state differently special case handling will be required.
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* - if activity/count is 0 then there are no active readers or writers
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* - if activity/count is +ve then that is the number of active readers
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* - if activity/count is -1 then there is one active writer
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*/
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#define SEM(rwp) ((struct rw_semaphore *)(rwp))
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#if defined(CONFIG_RWSEM_GENERIC_SPINLOCK)
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# define RW_COUNT(rwp) (SEM(rwp)->activity)
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# define rw_exit_locked(rwp) __up_read_locked(rwp)
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# define rw_tryenter_locked(rwp) __down_write_trylock_locked(rwp)
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extern void __up_read_locked(struct rw_semaphore *);
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extern int __down_write_trylock_locked(struct rw_semaphore *);
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#else
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# define RW_COUNT(rwp) (SEM(rwp)->count & RWSEM_ACTIVE_MASK)
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# define rw_exit_locked(rwp) up_read(rwp)
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# define rw_tryenter_locked(rwp) down_write_trylock(rwp)
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#endif
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static inline kthread_t *
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spl_rw_get_owner(krwlock_t *rwp)
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{
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return rwp->rw_owner;
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}
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static inline void
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spl_rw_set_owner(krwlock_t *rwp)
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{
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unsigned long flags;
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spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
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rwp->rw_owner = current;
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spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
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}
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static inline void
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spl_rw_clear_owner(krwlock_t *rwp)
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{
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unsigned long flags;
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spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
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rwp->rw_owner = NULL;
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spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
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}
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static inline kthread_t *
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rw_owner(krwlock_t *rwp)
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{
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unsigned long flags;
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kthread_t *owner;
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spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
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owner = spl_rw_get_owner(rwp);
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spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
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return owner;
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}
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static inline int
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RW_READ_HELD(krwlock_t *rwp)
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{
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unsigned long flags;
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int rc;
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spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
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rc = ((RW_COUNT(rwp) > 0) && (spl_rw_get_owner(rwp) == NULL));
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spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
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return rc;
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}
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static inline int
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RW_WRITE_HELD(krwlock_t *rwp)
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{
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unsigned long flags;
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int rc;
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spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
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rc = ((RW_COUNT(rwp) < 0) && (spl_rw_get_owner(rwp) == current));
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spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
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return rc;
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}
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static inline int
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RW_LOCK_HELD(krwlock_t *rwp)
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{
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unsigned long flags;
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int rc;
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spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
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rc = (RW_COUNT(rwp) != 0);
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spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
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return rc;
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}
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/*
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* The following functions must be a #define and not static inline.
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* This ensures that the native linux semaphore functions (down/up)
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* will be correctly located in the users code which is important
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* for the built in kernel lock analysis tools
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*/
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#define rw_init(rwp, name, type, arg) \
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({ \
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init_rwsem(SEM(rwp)); \
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spl_rw_clear_owner(rwp); \
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})
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#define rw_destroy(rwp) \
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({ \
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VERIFY(!RW_LOCK_HELD(rwp)); \
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})
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#define rw_tryenter(rwp, rw) \
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({ \
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int _rc_ = 0; \
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\
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switch (rw) { \
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case RW_READER: \
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_rc_ = down_read_trylock(SEM(rwp)); \
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break; \
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case RW_WRITER: \
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if ((_rc_ = down_write_trylock(SEM(rwp)))) \
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spl_rw_set_owner(rwp); \
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break; \
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default: \
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SBUG(); \
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} \
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_rc_; \
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})
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#define rw_enter(rwp, rw) \
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({ \
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switch (rw) { \
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case RW_READER: \
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down_read(SEM(rwp)); \
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break; \
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case RW_WRITER: \
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down_write(SEM(rwp)); \
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spl_rw_set_owner(rwp); \
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break; \
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default: \
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SBUG(); \
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} \
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})
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#define rw_exit(rwp) \
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({ \
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if (RW_WRITE_HELD(rwp)) { \
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spl_rw_clear_owner(rwp); \
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up_write(SEM(rwp)); \
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} else { \
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ASSERT(RW_READ_HELD(rwp)); \
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up_read(SEM(rwp)); \
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} \
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})
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#define rw_downgrade(rwp) \
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({ \
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spl_rw_clear_owner(rwp); \
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downgrade_write(SEM(rwp)); \
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})
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#define rw_tryupgrade(rwp) \
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({ \
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unsigned long _flags_; \
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int _rc_ = 0; \
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\
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spin_lock_irqsave(&SEM(rwp)->wait_lock, _flags_); \
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if (list_empty(&SEM(rwp)->wait_list) && (RW_COUNT(rwp) == 1)) { \
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rw_exit_locked(SEM(rwp)); \
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VERIFY(_rc_ = rw_tryenter_locked(SEM(rwp))); \
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(rwp)->rw_owner = current; \
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} \
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spin_unlock_irqrestore(&SEM(rwp)->wait_lock, _flags_); \
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_rc_; \
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})
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int spl_rw_init(void);
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void spl_rw_fini(void);
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#endif /* _SPL_RWLOCK_H */
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