Reimplement rwlocks for Linux lock profiling/analysis.

It turns out that the previous rwlock implementation worked well but
did not integrate properly with the upstream kernel lock profiling/
analysis tools.  This is a major problem since it would be awfully
nice to be able to use the automatic lock checker and profiler.

The problem is that the upstream lock tools use the pre-processor
to create a lock class for each uniquely named locked.  Since the
rwsem was embedded in a wrapper structure the name was always the
same.  The effect was that we only ended up with one lock class for
the entire SPL which caused the lock dependency checker to flag
nearly everything as a possible deadlock.

The solution was to directly map a krwlock to a Linux rwsem using
a typedef there by eliminating the wrapper structure.  This was not
done initially because the rwsem implementation is specific to the arch.
To fully implement the Solaris krwlock API using only the provided rwsem
API is not possible.  It can only be done by directly accessing some of
the internal data member of the rwsem structure.

For example, the Linux API provides a different function for dropping
a reader vs writer lock.  Whereas the Solaris API uses the same function
and the caller does not pass in what type of lock it is.  This means to
properly drop the lock we need to determine if the lock is currently a
reader or writer lock.  Then we need to call the proper Linux API function.
Unfortunately, there is no provided API for this so we must extracted this
information directly from arch specific lock implementation.  This is
all do able, and what I did, but it does complicate things considerably.

The good news is that in addition to the profiling benefits of this
change.  We may see performance improvements due to slightly reduced
overhead when creating rwlocks and manipulating them.

The only function I was forced to sacrafice was rw_owner() because this
information is simply not stored anywhere in the rwsem.  Luckily this
appears not to be a commonly used function on Solaris, and it is my
understanding it is mainly used for debugging anyway.

In addition to the core rwlock changes, extensive updates were made to
the rwlock regression tests.  Each class of test was extended to provide
more API coverage and to be more rigerous in checking for misbehavior.

This is a pretty significant change and with that in mind I have been
careful to validate it on several platforms before committing.  The full
SPLAT regression test suite was run numberous times on all of the following
platforms.  This includes various kernels ranging from 2.6.16 to 2.6.29.

- SLES10   (ppc64)
- SLES11   (x86_64)
- CHAOS4.2 (x86_64)
- RHEL5.3  (x86_64)
- RHEL6    (x86_64)
- FC11     (x86_64)

1 files changed, 29 insertions, 297 deletions

diff --git a/module/spl/spl-rwlock.c b/module/spl/spl-rwlock.c
index 07fc2aae4..8ff66bf9f 100644
--- a/module/spl/spl-rwlock.c
+++ b/module/spl/spl-rwlock.c
@@ -33,6 +33,11 @@
 #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;
@@ -40,322 +45,49 @@ struct rwsem_waiter {
 #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;
+        struct rwsem_waiter *waiter;
+        struct task_struct *tsk;
 
-	sem->activity = -1;
+        sem->activity = -1;
 
-	waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
-	list_del(&waiter->list);
+        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;
+        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 */
-static void
+void
 __up_read_locked(struct rw_semaphore *sem)
 {
-	if (--sem->activity == 0 && !list_empty(&sem->wait_list))
-		(void)__rwsem_wake_one_writer_locked(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 */
-static int
-__down_write_trylock_locked(struct rw_semaphore *sem)
-{
-	int ret = 0;
-
-	if (sem->activity == 0 && list_empty(&sem->wait_list)) {
-		/* granted */
-		sem->activity = -1;
-		ret = 1;
-	}
-
-	return ret;
-}
-#endif
-
-void
-__rw_init(krwlock_t *rwlp, char *name, krw_type_t type, void *arg)
-{
-	int flags = KM_SLEEP;
-
-        ASSERT(rwlp);
-        ASSERT(name);
-	ASSERT(type == RW_DEFAULT);	/* XXX no irq handler use */
-	ASSERT(arg == NULL);		/* XXX no irq handler use */
-
-	rwlp->rw_magic = RW_MAGIC;
-	rwlp->rw_owner = NULL;
-	rwlp->rw_name = NULL;
-        rwlp->rw_name_size = strlen(name) + 1;
-
-        /* We may be called when there is a non-zero preempt_count or
-         * interrupts are disabled is which case we must not sleep.
-         */
-        if (current_thread_info()->preempt_count || irqs_disabled())
-                flags = KM_NOSLEEP;
-
-        rwlp->rw_name = kmem_alloc(rwlp->rw_name_size, flags);
-        if (rwlp->rw_name == NULL)
-                return;
-
-	init_rwsem(&rwlp->rw_sem);
-        strcpy(rwlp->rw_name, name);
-}
-EXPORT_SYMBOL(__rw_init);
-
-void
-__rw_destroy(krwlock_t *rwlp)
-{
-	ASSERT(rwlp);
-	ASSERT(rwlp->rw_magic == RW_MAGIC);
-	ASSERT(rwlp->rw_owner == NULL);
-	spin_lock(&rwlp->rw_sem.wait_lock);
-	ASSERT(list_empty(&rwlp->rw_sem.wait_list));
-	spin_unlock(&rwlp->rw_sem.wait_lock);
-
-        kmem_free(rwlp->rw_name, rwlp->rw_name_size);
-
-	memset(rwlp, RW_POISON, sizeof(krwlock_t));
-}
-EXPORT_SYMBOL(__rw_destroy);
-
-/* Return 0 if the lock could not be obtained without blocking. */
 int
-__rw_tryenter(krwlock_t *rwlp, krw_t rw)
-{
-	int rc = 0;
-	ENTRY;
-
-	ASSERT(rwlp);
-	ASSERT(rwlp->rw_magic == RW_MAGIC);
-
-	switch (rw) {
-		/* these functions return 1 if success, 0 if contention */
-		case RW_READER:
-			/* Here the Solaris code would return 0
-			 * if there were any write waiters.  Specifically
-			 * thinking about the case where readers may have
-			 * the lock and we would also allow this thread
-			 * to grab the read lock with a writer waiting in the
-			 * queue. This doesn't seem like a correctness
-			 * issue, so just call down_read_trylock()
-			 * for the test.  We may have to revisit this if
-			 * it becomes an issue */
-			rc = down_read_trylock(&rwlp->rw_sem);
-			break;
-		case RW_WRITER:
-			rc = down_write_trylock(&rwlp->rw_sem);
-			if (rc) {
-				/* there better not be anyone else
-				 * holding the write lock here */
-				ASSERT(rwlp->rw_owner == NULL);
-				rwlp->rw_owner = current;
-			}
-			break;
-		default:
-			SBUG();
-	}
-
-	RETURN(rc);
-}
-EXPORT_SYMBOL(__rw_tryenter);
-
-void
-__rw_enter(krwlock_t *rwlp, krw_t rw)
-{
-	ENTRY;
-	ASSERT(rwlp);
-	ASSERT(rwlp->rw_magic == RW_MAGIC);
-
-	switch (rw) {
-		case RW_READER:
-			/* Here the Solaris code would block
-			 * if there were any write waiters.  Specifically
-			 * thinking about the case where readers may have
-			 * the lock and we would also allow this thread
-			 * to grab the read lock with a writer waiting in the
-			 * queue. This doesn't seem like a correctness
-			 * issue, so just call down_read()
-			 * for the test.  We may have to revisit this if
-			 * it becomes an issue */
-			down_read(&rwlp->rw_sem);
-			break;
-		case RW_WRITER:
-			down_write(&rwlp->rw_sem);
-
-			/* there better not be anyone else
-			 * holding the write lock here */
-			ASSERT(rwlp->rw_owner == NULL);
-			rwlp->rw_owner = current;
-			break;
-		default:
-			SBUG();
-	}
-	EXIT;
-}
-EXPORT_SYMBOL(__rw_enter);
-
-void
-__rw_exit(krwlock_t *rwlp)
-{
-	ENTRY;
-	ASSERT(rwlp);
-	ASSERT(rwlp->rw_magic == RW_MAGIC);
-
-	/* rw_owner is held by current
-	 * thread iff it is a writer */
-	if (rwlp->rw_owner == current) {
-		rwlp->rw_owner = NULL;
-		up_write(&rwlp->rw_sem);
-	} else {
-		up_read(&rwlp->rw_sem);
-	}
-	EXIT;
-}
-EXPORT_SYMBOL(__rw_exit);
-
-void
-__rw_downgrade(krwlock_t *rwlp)
-{
-	ENTRY;
-	ASSERT(rwlp);
-	ASSERT(rwlp->rw_magic == RW_MAGIC);
-	ASSERT(rwlp->rw_owner == current);
-
-	rwlp->rw_owner = NULL;
-	downgrade_write(&rwlp->rw_sem);
-	EXIT;
-}
-EXPORT_SYMBOL(__rw_downgrade);
-
-/* Return 0 if unable to perform the upgrade.
- * Might be wise to fix the caller
- * to acquire the write lock first?
- */
-int
-__rw_tryupgrade(krwlock_t *rwlp)
-{
-	int rc = 0;
-	ENTRY;
-
-	ASSERT(rwlp);
-	ASSERT(rwlp->rw_magic == RW_MAGIC);
-
-	spin_lock(&rwlp->rw_sem.wait_lock);
-
-	/* Check if there is anyone waiting for the
-	 * lock.  If there is, then we know we should
-	 * not try to upgrade the lock */
-	if (!list_empty(&rwlp->rw_sem.wait_list)) {
-		spin_unlock(&rwlp->rw_sem.wait_lock);
-		RETURN(0);
-	}
-#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
-	/* Note that activity is protected by
-	 * the wait_lock.  Don't try to upgrade
-	 * if there are multiple readers currently
-	 * holding the lock */
-	if (rwlp->rw_sem.activity > 1) {
-#else
-	/* Don't try to upgrade
-	 * if there are multiple readers currently
-	 * holding the lock */
-	if ((rwlp->rw_sem.count & RWSEM_ACTIVE_MASK) > 1) {
-#endif
-		spin_unlock(&rwlp->rw_sem.wait_lock);
-		RETURN(0);
-	}
-
-#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
-	/* Here it should be safe to drop the
-	 * read lock and reacquire it for writing since
-	 * we know there are no waiters */
-	__up_read_locked(&rwlp->rw_sem);
-
-	/* returns 1 if success, 0 if contention */
-	rc = __down_write_trylock_locked(&rwlp->rw_sem);
-#else
-	/* Here it should be safe to drop the
-	 * read lock and reacquire it for writing since
-	 * we know there are no waiters */
-	up_read(&rwlp->rw_sem);
-
-	/* returns 1 if success, 0 if contention */
-	rc = down_write_trylock(&rwlp->rw_sem);
-#endif
-
-	/* Check if upgrade failed.  Should not ever happen
-	 * if we got to this point */
-	ASSERT(rc);
-	ASSERT(rwlp->rw_owner == NULL);
-	rwlp->rw_owner = current;
-	spin_unlock(&rwlp->rw_sem.wait_lock);
-
-	RETURN(1);
-}
-EXPORT_SYMBOL(__rw_tryupgrade);
-
-kthread_t *
-__rw_owner(krwlock_t *rwlp)
+__down_write_trylock_locked(struct rw_semaphore *sem)
 {
-	ENTRY;
-	ASSERT(rwlp);
-	ASSERT(rwlp->rw_magic == RW_MAGIC);
-	RETURN(rwlp->rw_owner);
-}
-EXPORT_SYMBOL(__rw_owner);
+        int ret = 0;
 
-int
-__rw_read_held(krwlock_t *rwlp)
-{
-	ENTRY;
-	ASSERT(rwlp);
-	ASSERT(rwlp->rw_magic == RW_MAGIC);
-	RETURN(__rw_lock_held(rwlp) && rwlp->rw_owner == NULL);
-}
-EXPORT_SYMBOL(__rw_read_held);
+        if (sem->activity == 0 && list_empty(&sem->wait_list)) {
+                sem->activity = -1;
+                ret = 1;
+        }
 
-int
-__rw_write_held(krwlock_t *rwlp)
-{
-	ENTRY;
-	ASSERT(rwlp);
-	ASSERT(rwlp->rw_magic == RW_MAGIC);
-	RETURN(rwlp->rw_owner == current);
+        return ret;
 }
-EXPORT_SYMBOL(__rw_write_held);
-
-int
-__rw_lock_held(krwlock_t *rwlp)
-{
-	int rc = 0;
-	ENTRY;
+EXPORT_SYMBOL(__down_write_trylock_locked);
 
-	ASSERT(rwlp);
-	ASSERT(rwlp->rw_magic == RW_MAGIC);
-
-	spin_lock_irq(&(rwlp->rw_sem.wait_lock));
-#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
-	if (rwlp->rw_sem.activity != 0) {
-#else
-	if (rwlp->rw_sem.count != 0) {
 #endif
-		rc = 1;
-	}
-
-	spin_unlock_irq(&(rwlp->rw_sem.wait_lock));
-
-	RETURN(rc);
-}
-EXPORT_SYMBOL(__rw_lock_held);