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Subject[PATCH v2] lockdep: Add helper function for dir vs file i_mutex annotation
Purely in-memory filesystems do not use the inode hash as the dcache tells
us if an entry already exists. As a result, they do not call
unlock_new_inode. If CONFIG_DEBUG_LOCK_ALLOC is set, this can lead to
false positives from lockdep like below:

| find/645 is trying to acquire lock:
| (&mm->mmap_sem){++++++}, at: [<ffffffff81109514>] might_fault+0x5c/0xac
|
| but task is already holding lock:
| (&sb->s_type->i_mutex_key#15){+.+.+.}, at: [<ffffffff81149f34>]
| vfs_readdir+0x5b/0xb4
|
| which lock already depends on the new lock.
|
| the existing dependency chain (in reverse order) is:
|
| -> #1 (&sb->s_type->i_mutex_key#15){+.+.+.}:
| [<ffffffff8108ac26>] lock_acquire+0xbf/0x103
| [<ffffffff814db822>] __mutex_lock_common+0x4c/0x361
| [<ffffffff814dbc46>] mutex_lock_nested+0x40/0x45
| [<ffffffff811daa87>] hugetlbfs_file_mmap+0x82/0x110
| [<ffffffff81111557>] mmap_region+0x258/0x432
| [<ffffffff811119dd>] do_mmap_pgoff+0x2ac/0x306
| [<ffffffff81111b4f>] sys_mmap_pgoff+0x118/0x16a
| [<ffffffff8100c858>] sys_mmap+0x22/0x24
| [<ffffffff814e3ec2>] system_call_fastpath+0x16/0x1b
|
| -> #0 (&mm->mmap_sem){++++++}:
| [<ffffffff8108a4bc>] __lock_acquire+0xa1a/0xcf7
| [<ffffffff8108ac26>] lock_acquire+0xbf/0x103
| [<ffffffff81109541>] might_fault+0x89/0xac
| [<ffffffff81149cff>] filldir+0x6f/0xc7
| [<ffffffff811586ea>] dcache_readdir+0x67/0x205
| [<ffffffff81149f54>] vfs_readdir+0x7b/0xb4
| [<ffffffff8114a073>] sys_getdents+0x7e/0xd1
| [<ffffffff814e3ec2>] system_call_fastpath+0x16/0x1b

This moves the directory vs file lockdep annotation into a helper function
that can be called by in-memory filesystems and has hugetlbfs call it.

Signed-off-by: Josh Boyer <jwboyer@redhat.com>
---
v2: Make the helper an empty inline in the non-debug case to cleanup some ifdefs
fs/hugetlbfs/inode.c | 1 +
fs/inode.c | 24 +++++++++++++++---------
include/linux/fs.h | 5 +++++
3 files changed, 21 insertions(+), 9 deletions(-)
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 87b6e04..ec88953 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -491,6 +491,7 @@ static struct inode *hugetlbfs_get_inode(struct super_block *sb, uid_t uid,
inode->i_op = &page_symlink_inode_operations;
break;
}
+ lockdep_annotate_inode_mutex_key(inode);
}
return inode;
}
diff --git a/fs/inode.c b/fs/inode.c
index 73920d5..ec79246 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -848,16 +848,9 @@ struct inode *new_inode(struct super_block *sb)
}
EXPORT_SYMBOL(new_inode);

-/**
- * unlock_new_inode - clear the I_NEW state and wake up any waiters
- * @inode: new inode to unlock
- *
- * Called when the inode is fully initialised to clear the new state of the
- * inode and wake up anyone waiting for the inode to finish initialisation.
- */
-void unlock_new_inode(struct inode *inode)
-{
#ifdef CONFIG_DEBUG_LOCK_ALLOC
+void lockdep_annotate_inode_mutex_key(struct inode *inode)
+{
if (S_ISDIR(inode->i_mode)) {
struct file_system_type *type = inode->i_sb->s_type;

@@ -873,7 +866,20 @@ void unlock_new_inode(struct inode *inode)
&type->i_mutex_dir_key);
}
}
+}
+EXPORT_SYMBOL(lockdep_annotate_inode_mutex_key);
#endif
+
+/**
+ * unlock_new_inode - clear the I_NEW state and wake up any waiters
+ * @inode: new inode to unlock
+ *
+ * Called when the inode is fully initialised to clear the new state of the
+ * inode and wake up anyone waiting for the inode to finish initialisation.
+ */
+void unlock_new_inode(struct inode *inode)
+{
+ lockdep_annotate_inode_mutex_key(inode);
spin_lock(&inode->i_lock);
WARN_ON(!(inode->i_state & I_NEW));
inode->i_state &= ~I_NEW;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 178cdb4..c2bd68f 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2318,6 +2318,11 @@ extern struct inode * iget5_locked(struct super_block *, unsigned long, int (*te
extern struct inode * iget_locked(struct super_block *, unsigned long);
extern int insert_inode_locked4(struct inode *, unsigned long, int (*test)(struct inode *, void *), void *);
extern int insert_inode_locked(struct inode *);
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+extern void lockdep_annotate_inode_mutex_key(struct inode *inode);
+#else
+static inline void lockdep_annotate_inode_mutex_key(struct inode *inode) { };
+#endif
extern void unlock_new_inode(struct inode *);
extern unsigned int get_next_ino(void);

--
1.7.6


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