diff options
| -rw-r--r-- | include/sys/rwlock.h | 50 | ||||
| -rw-r--r-- | module/spl/spl-rwlock.c | 60 | ||||
| -rw-r--r-- | module/splat/splat-rwlock.c | 6 |
3 files changed, 16 insertions, 100 deletions
diff --git a/include/sys/rwlock.h b/include/sys/rwlock.h index c82764ce9..14d097b01 100644 --- a/include/sys/rwlock.h +++ b/include/sys/rwlock.h @@ -208,49 +208,31 @@ RW_LOCK_HELD(krwlock_t *rwp) spl_rw_lockdep_on_maybe(rwp); \ }) -#if defined(CONFIG_RWSEM_GENERIC_SPINLOCK) -#ifdef CONFIG_RWSEM_SPIN_ON_OWNER -#error spinlock rwsem should not have spin on owner -#endif /* - * For the generic implementations of rw-semaphores the following is - * true. If your semaphore implementation internally represents the - * semaphore state differently then special case handling is required. - * - if activity/count is 0 then there are no active readers or writers - * - if activity/count is +ve then that is the number of active readers - * - if activity/count is -1 then there is one active writer + * This implementation of rw_tryupgrade() behaves slightly differently + * from its counterparts on other platforms. It drops the RW_READER lock + * and then acquires the RW_WRITER lock leaving a small window where no + * lock is held. On other platforms the lock is never released during + * the upgrade process. This is necessary under Linux because the kernel + * does not provide an upgrade function. */ - -extern void __up_read_locked(struct rw_semaphore *); -extern int __down_write_trylock_locked(struct rw_semaphore *); - #define rw_tryupgrade(rwp) \ ({ \ - unsigned long _flags_; \ int _rc_ = 0; \ \ - spl_rw_lockdep_off_maybe(rwp); \ - spl_rwsem_lock_irqsave(&SEM(rwp)->wait_lock, _flags_); \ - if ((list_empty(&SEM(rwp)->wait_list)) && \ - (SEM(rwp)->activity == 1)) { \ - __up_read_locked(SEM(rwp)); \ - VERIFY(_rc_ = __down_write_trylock_locked(SEM(rwp))); \ - (rwp)->rw_owner = current; \ + if (RW_WRITE_HELD(rwp)) { \ + _rc_ = 1; \ + } else { \ + rw_exit(rwp); \ + if (rw_tryenter(rwp, RW_WRITER)) { \ + _rc_ = 1; \ + } else { \ + rw_enter(rwp, RW_READER); \ + _rc_ = 0; \ + } \ } \ - spl_rwsem_unlock_irqrestore(&SEM(rwp)->wait_lock, _flags_); \ - spl_rw_lockdep_on_maybe(rwp); \ _rc_; \ }) -#else -/* - * rw_tryupgrade() can be implemented correctly but for each supported - * arch we will need a custom implementation. For the x86 implementation - * it looks like a custom cmpxchg() to atomically check and promote the - * rwsem would be safe. For now that's not worth the trouble so in this - * case rw_tryupgrade() has just been disabled. - */ -#define rw_tryupgrade(rwp) ({ 0; }) -#endif int spl_rw_init(void); void spl_rw_fini(void); diff --git a/module/spl/spl-rwlock.c b/module/spl/spl-rwlock.c index 462a6f0de..98251c011 100644 --- a/module/spl/spl-rwlock.c +++ b/module/spl/spl-rwlock.c @@ -32,65 +32,5 @@ #define DEBUG_SUBSYSTEM S_RWLOCK -#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK - -/* - * From lib/rwsem-spinlock.c but modified such that the caller is - * responsible for acquiring and dropping the sem->wait_lock. - */ -struct rwsem_waiter { - struct list_head list; - struct task_struct *task; - unsigned int flags; -#define RWSEM_WAITING_FOR_READ 0x00000001 -#define RWSEM_WAITING_FOR_WRITE 0x00000002 -}; - -/* wake a single writer */ -static struct rw_semaphore * -__rwsem_wake_one_writer_locked(struct rw_semaphore *sem) -{ - struct rwsem_waiter *waiter; - struct task_struct *tsk; - - sem->activity = -1; - - waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); - list_del(&waiter->list); - - tsk = waiter->task; - smp_mb(); - waiter->task = NULL; - wake_up_process(tsk); - put_task_struct(tsk); - return sem; -} - -/* release a read lock on the semaphore */ -void -__up_read_locked(struct rw_semaphore *sem) -{ - if (--sem->activity == 0 && !list_empty(&sem->wait_list)) - (void)__rwsem_wake_one_writer_locked(sem); -} -EXPORT_SYMBOL(__up_read_locked); - -/* trylock for writing -- returns 1 if successful, 0 if contention */ -int -__down_write_trylock_locked(struct rw_semaphore *sem) -{ - int ret = 0; - - if (sem->activity == 0 && list_empty(&sem->wait_list)) { - sem->activity = -1; - ret = 1; - } - - return ret; -} -EXPORT_SYMBOL(__down_write_trylock_locked); - -#endif - int spl_rw_init(void) { return 0; } void spl_rw_fini(void) { } diff --git a/module/splat/splat-rwlock.c b/module/splat/splat-rwlock.c index 284f77370..abd6a0e60 100644 --- a/module/splat/splat-rwlock.c +++ b/module/splat/splat-rwlock.c @@ -588,7 +588,6 @@ splat_rwlock_test6(struct file *file, void *arg) goto out; } -#if defined(CONFIG_RWSEM_GENERIC_SPINLOCK) /* With one reader upgrade should never fail. */ rc = rw_tryupgrade(&rwp->rw_rwlock); if (!rc) { @@ -610,11 +609,6 @@ splat_rwlock_test6(struct file *file, void *arg) rc = 0; splat_vprint(file, SPLAT_RWLOCK_TEST6_NAME, "%s", "rwlock properly upgraded\n"); -#else - rc = 0; - splat_vprint(file, SPLAT_RWLOCK_TEST6_NAME, "%s", - "rw_tryupgrade() is disabled for this arch\n"); -#endif out: rw_exit(&rwp->rw_rwlock); rw_destroy(&rwp->rw_rwlock); |