From 14358e6ddaed27499d7d366b3e65c3e46b39e1c4 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Sun, 14 Oct 2007 01:38:33 +0200 Subject: [PATCH] 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 --- fs/inode.c | 12 ++++++++++++ include/linux/fs.h | 1 + 2 files changed, 13 insertions(+) diff --git a/fs/inode.c b/fs/inode.c index bf6adf122c68..f97de0aeb3b6 100644 --- 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 0cad20e12585..6d760f1ad875 100644 --- 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; };