logfs: fix "Kernel BUG at readwrite.c:1193"

This happens when __logfs_create() tries to write a new inode to the disk
which is full.

__logfs_create() associates the transaction pointer with inode.  During
the logfs_write_inode() function call chain this transaction pointer is
moved from inode to page->private using function move_inode_to_page
(do_write_inode() -> inode_to_page() -> move_inode_to_page)

When the write inode fails, the transaction is aborted and iput is called
on the failed inode.  During delete_inode the same transaction pointer
associated with the page is getting used.  Thus causing kernel BUG.

The patch checks for error in write_inode() and restores the page->private
to NULL.

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=20162

Signed-off-by: Prasad Joshi <prasadjoshi124@gmail.com>
Cc: Joern Engel <joern@logfs.org>
Cc: Florian Mickler <florian@mickler.org>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Maciej Rutecki <maciej.rutecki@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/logfs/readwrite.c

@@ -1994,6 +1994,9 @@ static int do_write_inode(struct inode *inode)
 
 	/* FIXME: transaction is part of logfs_block now.  Is that enough? */
 	err = logfs_write_buf(master_inode, page, 0);
+	if (err)
+		move_page_to_inode(inode, page);
+
 	logfs_put_write_page(page);
 	return err;
 }