debugfs: annotate debugfs handlers vs. removal with lockdep

When you take a lock in a debugfs handler but also try
to remove the debugfs file under that lock, things can
deadlock since the removal has to wait for all users
to finish.

Add lockdep annotations in debugfs_file_get()/_put()
to catch such issues.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index e00189aebbf4abd9e932ac810fc1937c20fad755..3eff92450fd58c3cf277b21994770ca05c2bbab4 100644 (file)
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -108,6 +108,12 @@ int debugfs_file_get(struct dentry *dentry)
                        kfree(fsd);
                        fsd = READ_ONCE(dentry->d_fsdata);
                }
+#ifdef CONFIG_LOCKDEP
+               fsd->lock_name = kasprintf(GFP_KERNEL, "debugfs:%pd", dentry);
+               lockdep_register_key(&fsd->key);
+               lockdep_init_map(&fsd->lockdep_map, fsd->lock_name ?: "debugfs",
+                                &fsd->key, 0);
+#endif
        }
 
        /*
@@ -124,6 +130,8 @@ int debugfs_file_get(struct dentry *dentry)
        if (!refcount_inc_not_zero(&fsd->active_users))
                return -EIO;
 
+       lock_map_acquire_read(&fsd->lockdep_map);
+
        return 0;
 }
 EXPORT_SYMBOL_GPL(debugfs_file_get);
@@ -141,6 +149,8 @@ void debugfs_file_put(struct dentry *dentry)
 {
        struct debugfs_fsdata *fsd = READ_ONCE(dentry->d_fsdata);
 
+       lock_map_release(&fsd->lockdep_map);
+
        if (refcount_dec_and_test(&fsd->active_users))
                complete(&fsd->active_users_drained);
 }

diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index dcde4199a625d885bf3f21cb73923f18828ade15..80f4f000dcc138a405b940041f3219bfe7a49005 100644 (file)
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -241,6 +241,14 @@ static void debugfs_release_dentry(struct dentry *dentry)
        if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)
                return;
 
+       /* check it wasn't a dir (no fsdata) or automount (no real_fops) */
+       if (fsd && fsd->real_fops) {
+#ifdef CONFIG_LOCKDEP
+               lockdep_unregister_key(&fsd->key);
+               kfree(fsd->lock_name);
+#endif
+       }
+
        kfree(fsd);
 }
 
@@ -744,6 +752,10 @@ static void __debugfs_file_removed(struct dentry *dentry)
        fsd = READ_ONCE(dentry->d_fsdata);
        if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)
                return;
+
+       lock_map_acquire(&fsd->lockdep_map);
+       lock_map_release(&fsd->lockdep_map);
+
        if (!refcount_dec_and_test(&fsd->active_users))
                wait_for_completion(&fsd->active_users_drained);
 }

diff --git a/fs/debugfs/internal.h b/fs/debugfs/internal.h
index f7c489b5a368c6469be1952c3ca421561a0ac29c..c7d61cfc97d264ba674dc3cb32c2e29ae4af1ba0 100644 (file)
--- a/fs/debugfs/internal.h
+++ b/fs/debugfs/internal.h
@@ -7,6 +7,7 @@
 
 #ifndef _DEBUGFS_INTERNAL_H_
 #define _DEBUGFS_INTERNAL_H_
+#include <linux/lockdep.h>
 
 struct file_operations;
 
@@ -23,6 +24,11 @@ struct debugfs_fsdata {
                struct {
                        refcount_t active_users;
                        struct completion active_users_drained;
+#ifdef CONFIG_LOCKDEP
+                       struct lockdep_map lockdep_map;
+                       struct lock_class_key key;
+                       char *lock_name;
+#endif
                };
        };
 };