lockdep: annotate dir vs file i_mutex
On Mon, 2007-09-24 at 22:13 -0400, Steven Rostedt wrote:
> The circular lock seems to be this:
>
> #1:
>
> sys_mmap2: down_write(&mm->mmap_sem);
> nfs_revalidate_mapping: mutex_lock(&inode->i_mutex);
>
>
> #0:
>
> vfs_readdir: mutex_lock(&inode->i_mutex);
> - during the readdir (filldir64), we take a user fault (missing page?)
> and call do_page_fault -
> do_page_fault: down_read(&mm->mmap_sem);
>
>
> So it does indeed look like a circular locking. Now the question is, "is
> this a bug?". Looking like the inode of #1 must be a file or something
> else that you can mmap and the inode of #0 seems it must be a directory.
> I would say "no".
>
> Now if you can readdir on a file or mmap a directory, then this could be
> an issue.
>
> Otherwise, I'd love to see someone teach lockdep about this issue! ;-)
Make a distinction between file and dir usage of i_mutex.
The inode should be complete and unused at unlock_new_inode(), re-init
i_mutex depending on its type.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
diff --git a/fs/inode.c b/fs/inode.c
index bf6adf1..f97de0a 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -567,6 +567,18 @@
void unlock_new_inode(struct inode *inode)
{
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+ struct file_system_type *type = inode->i_sb->s_type;
+ /*
+ * ensure nobody is actually holding i_mutex
+ */
+ mutex_destroy(&inode->i_mutex);
+ mutex_init(&inode->i_mutex);
+ if (inode->i_mode & S_IFDIR)
+ lockdep_set_class(&inode->i_mutex, &type->i_mutex_dir_key);
+ else
+ lockdep_set_class(&inode->i_mutex, &type->i_mutex_key);
+#endif
/*
* This is special! We do not need the spinlock
* when clearing I_LOCK, because we're guaranteed
