Commit f4acfcd4 authored by Johannes Berg's avatar Johannes Berg
Browse files

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: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarJohannes Berg <johannes.berg@intel.com>
parent 0ed04a18

fs/debugfs/file.c

+10 −0
Original line number Diff line number Diff line
@@ -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);

}

fs/debugfs/inode.c

+12 −0
Original line number Diff line number Diff line
@@ -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);

}

fs/debugfs/internal.h

+6 −0
Original line number Diff line number Diff line
@@ -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

		};

	};

};