1 files changed, 106 insertions, 7 deletions

diff --git a/fs/afs/fs_operation.c b/fs/afs/fs_operation.c
index 428721bbe4f6..8418813ee043 100644
--- a/fs/afs/fs_operation.c
+++ b/fs/afs/fs_operation.c
@@ -49,6 +49,105 @@ struct afs_operation *afs_alloc_operation(struct key *key, struct afs_volume *vo
 	return op;
 }
 
+struct afs_io_locker {
+	struct list_head	link;
+	struct task_struct	*task;
+	unsigned long		have_lock;
+};
+
+/*
+ * Unlock the I/O lock on a vnode.
+ */
+static void afs_unlock_for_io(struct afs_vnode *vnode)
+{
+	struct afs_io_locker *locker;
+
+	spin_lock(&vnode->lock);
+	locker = list_first_entry_or_null(&vnode->io_lock_waiters,
+					  struct afs_io_locker, link);
+	if (locker) {
+		list_del(&locker->link);
+		smp_store_release(&locker->have_lock, 1); /* The unlock barrier. */
+		smp_mb__after_atomic(); /* Store have_lock before task state */
+		wake_up_process(locker->task);
+	} else {
+		clear_bit(AFS_VNODE_IO_LOCK, &vnode->flags);
+	}
+	spin_unlock(&vnode->lock);
+}
+
+/*
+ * Lock the I/O lock on a vnode uninterruptibly.  We can't use an ordinary
+ * mutex as lockdep will complain if we unlock it in the wrong thread.
+ */
+static void afs_lock_for_io(struct afs_vnode *vnode)
+{
+	struct afs_io_locker myself = { .task = current, };
+
+	spin_lock(&vnode->lock);
+
+	if (!test_and_set_bit(AFS_VNODE_IO_LOCK, &vnode->flags)) {
+		spin_unlock(&vnode->lock);
+		return;
+	}
+
+	list_add_tail(&myself.link, &vnode->io_lock_waiters);
+	spin_unlock(&vnode->lock);
+
+	for (;;) {
+		set_current_state(TASK_UNINTERRUPTIBLE);
+		if (smp_load_acquire(&myself.have_lock)) /* The lock barrier */
+			break;
+		schedule();
+	}
+	__set_current_state(TASK_RUNNING);
+}
+
+/*
+ * Lock the I/O lock on a vnode interruptibly.  We can't use an ordinary mutex
+ * as lockdep will complain if we unlock it in the wrong thread.
+ */
+static int afs_lock_for_io_interruptible(struct afs_vnode *vnode)
+{
+	struct afs_io_locker myself = { .task = current, };
+	int ret = 0;
+
+	spin_lock(&vnode->lock);
+
+	if (!test_and_set_bit(AFS_VNODE_IO_LOCK, &vnode->flags)) {
+		spin_unlock(&vnode->lock);
+		return 0;
+	}
+
+	list_add_tail(&myself.link, &vnode->io_lock_waiters);
+	spin_unlock(&vnode->lock);
+
+	for (;;) {
+		set_current_state(TASK_INTERRUPTIBLE);
+		if (smp_load_acquire(&myself.have_lock) || /* The lock barrier */
+		    signal_pending(current))
+			break;
+		schedule();
+	}
+	__set_current_state(TASK_RUNNING);
+
+	/* If we got a signal, try to transfer the lock onto the next
+	 * waiter.
+	 */
+	if (unlikely(signal_pending(current))) {
+		spin_lock(&vnode->lock);
+		if (myself.have_lock) {
+			spin_unlock(&vnode->lock);
+			afs_unlock_for_io(vnode);
+		} else {
+			list_del(&myself.link);
+			spin_unlock(&vnode->lock);
+		}
+		ret = -ERESTARTSYS;
+	}
+	return ret;
+}
+
 /*
  * Lock the vnode(s) being operated upon.
  */
@@ -60,7 +159,7 @@ static bool afs_get_io_locks(struct afs_operation *op)
 	_enter("");
 
 	if (op->flags & AFS_OPERATION_UNINTR) {
-		mutex_lock(&vnode->io_lock);
+		afs_lock_for_io(vnode);
 		op->flags |= AFS_OPERATION_LOCK_0;
 		_leave(" = t [1]");
 		return true;
@@ -72,7 +171,7 @@ static bool afs_get_io_locks(struct afs_operation *op)
 	if (vnode2 > vnode)
 		swap(vnode, vnode2);
 
-	if (mutex_lock_interruptible(&vnode->io_lock) < 0) {
+	if (afs_lock_for_io_interruptible(vnode) < 0) {
 		afs_op_set_error(op, -ERESTARTSYS);
 		op->flags |= AFS_OPERATION_STOP;
 		_leave(" = f [I 0]");
@@ -81,10 +180,10 @@ static bool afs_get_io_locks(struct afs_operation *op)
 	op->flags |= AFS_OPERATION_LOCK_0;
 
 	if (vnode2) {
-		if (mutex_lock_interruptible_nested(&vnode2->io_lock, 1) < 0) {
+		if (afs_lock_for_io_interruptible(vnode2) < 0) {
 			afs_op_set_error(op, -ERESTARTSYS);
 			op->flags |= AFS_OPERATION_STOP;
-			mutex_unlock(&vnode->io_lock);
+			afs_unlock_for_io(vnode);
 			op->flags &= ~AFS_OPERATION_LOCK_0;
 			_leave(" = f [I 1]");
 			return false;
@@ -104,9 +203,9 @@ static void afs_drop_io_locks(struct afs_operation *op)
 	_enter("");
 
 	if (op->flags & AFS_OPERATION_LOCK_1)
-		mutex_unlock(&vnode2->io_lock);
+		afs_unlock_for_io(vnode2);
 	if (op->flags & AFS_OPERATION_LOCK_0)
-		mutex_unlock(&vnode->io_lock);
+		afs_unlock_for_io(vnode);
 }
 
 static void afs_prepare_vnode(struct afs_operation *op, struct afs_vnode_param *vp,
@@ -157,7 +256,7 @@ bool afs_begin_vnode_operation(struct afs_operation *op)
 /*
  * Tidy up a filesystem cursor and unlock the vnode.
  */
-static void afs_end_vnode_operation(struct afs_operation *op)
+void afs_end_vnode_operation(struct afs_operation *op)
 {
 	_enter("");