btrfs: add and use helper to verify the calling task has locked the inode

We have a few places that check if we have the inode locked by doing:

    ASSERT(inode_is_locked(vfs_inode));

This actually proved to be useful several times as if assertions are
enabled (and by default they are in many distros) it immediately triggers
a crash which is impossible for users to miss.

However that doesn't check if the lock is held by the calling task, so
the check passes if some other task locked the inode.

Using one of the lockdep functions to check the lock is held, like
lockdep_assert_held() for example, does check that the calling task
holds the lock, and if that's not the case it produces a warning and
stack trace in dmesg. However, despite the misleading "assert" in the
name of the lockdep helpers, it does not trigger a crash/BUG_ON(), just
a warning and splat in dmesg, which is easy to get unnoticed by users
who may have lockdep enabled.

So add a helper that does the ASSERT() and calls lockdep_assert_held()
immediately after and use it every where we check the inode is locked.
Like this if the lock is held by some other task we get the warning
in dmesg which is caught by fstests, very helpful during development,
and may also be occassionaly noticed by users with lockdep enabled.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/btrfs_inode.h

@@ -505,6 +505,14 @@ static inline bool btrfs_inode_can_compress(const struct btrfs_inode *inode)
 	return true;
 }
 
+static inline void btrfs_assert_inode_locked(struct btrfs_inode *inode)
+{
+	/* Immediately trigger a crash if the inode is not locked. */
+	ASSERT(inode_is_locked(&inode->vfs_inode));
+	/* Trigger a splat in dmesg if this task is not holding the lock. */
+	lockdep_assert_held(&inode->vfs_inode.i_rwsem);
+}
+
 /* Array of bytes with variable length, hexadecimal format 0x1234 */
 #define CSUM_FMT				"0x%*phN"
 #define CSUM_FMT_VALUE(size, bytes)		size, bytes

fs/btrfs/file.c

@@ -1617,7 +1617,7 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 	if (current->journal_info == BTRFS_TRANS_DIO_WRITE_STUB) {
 		skip_ilock = true;
 		current->journal_info = NULL;
-		lockdep_assert_held(&inode->vfs_inode.i_rwsem);
+		btrfs_assert_inode_locked(inode);
 	}
 
 	trace_btrfs_sync_file(file, datasync);

fs/btrfs/ordered-data.c

@@ -1015,7 +1015,7 @@ void btrfs_get_ordered_extents_for_logging(struct btrfs_inode *inode,
 {
 	struct rb_node *n;
 
-	ASSERT(inode_is_locked(&inode->vfs_inode));
+	btrfs_assert_inode_locked(inode);
 
 	spin_lock_irq(&inode->ordered_tree_lock);
 	for (n = rb_first(&inode->ordered_tree); n; n = rb_next(n)) {

fs/btrfs/tree-log.c

@@ -2877,7 +2877,7 @@ void btrfs_release_log_ctx_extents(struct btrfs_log_ctx *ctx)
 	struct btrfs_ordered_extent *ordered;
 	struct btrfs_ordered_extent *tmp;
 
-	ASSERT(inode_is_locked(&ctx->inode->vfs_inode));
+	btrfs_assert_inode_locked(ctx->inode);
 
 	list_for_each_entry_safe(ordered, tmp, &ctx->ordered_extents, log_list) {
 		list_del_init(&ordered->log_list);

fs/btrfs/verity.c

@@ -460,7 +460,7 @@ static int rollback_verity(struct btrfs_inode *inode)
 	struct btrfs_root *root = inode->root;
 	int ret;
 
-	ASSERT(inode_is_locked(&inode->vfs_inode));
+	btrfs_assert_inode_locked(inode);
 	truncate_inode_pages(inode->vfs_inode.i_mapping, inode->vfs_inode.i_size);
 	clear_bit(BTRFS_INODE_VERITY_IN_PROGRESS, &inode->runtime_flags);
 	ret = btrfs_drop_verity_items(inode);
@@ -585,7 +585,7 @@ static int btrfs_begin_enable_verity(struct file *filp)
 	struct btrfs_trans_handle *trans;
 	int ret;
 
-	ASSERT(inode_is_locked(file_inode(filp)));
+	btrfs_assert_inode_locked(inode);
 
 	if (test_bit(BTRFS_INODE_VERITY_IN_PROGRESS, &inode->runtime_flags))
 		return -EBUSY;
@@ -633,7 +633,7 @@ static int btrfs_end_enable_verity(struct file *filp, const void *desc,
 	int ret = 0;
 	int rollback_ret;
 
-	ASSERT(inode_is_locked(file_inode(filp)));
+	btrfs_assert_inode_locked(inode);
 
 	if (desc == NULL)
 		goto rollback;

fs/btrfs/xattr.c

@@ -120,7 +120,7 @@ int btrfs_setxattr(struct btrfs_trans_handle *trans, struct inode *inode,
 	 * locks the inode's i_mutex before calling setxattr or removexattr.
 	 */
 	if (flags & XATTR_REPLACE) {
-		ASSERT(inode_is_locked(inode));
+		btrfs_assert_inode_locked(BTRFS_I(inode));
 		di = btrfs_lookup_xattr(NULL, root, path,
 				btrfs_ino(BTRFS_I(inode)), name, name_len, 0);
 		if (!di)