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 bf6adf122c688b337abf5d7c00288857b74a5927..f97de0aeb3b69dcd320668ccbf6bbeb6e9d57932 100644 (file)
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -567,6 +567,18 @@ EXPORT_SYMBOL(new_inode);
 
 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

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0cad20e125852527f4c243b82922966e218fcce5..6d760f1ad87521c932d12d649cc0171d8e14f696 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1308,6 +1308,7 @@ struct file_system_type {
 
        struct lock_class_key i_lock_key;
        struct lock_class_key i_mutex_key;
+       struct lock_class_key i_mutex_dir_key;
        struct lock_class_key i_alloc_sem_key;
 };