[PATCH AUTOSEL 5.15 07/10] debugfs: annotate debugfs handlers vs. removal with lockdep

Sasha Levin
2023-12-04T20:39:40Z

From: Johannes Berg <johannes.berg@intel.com>

[ Upstream commit f4acfcd4deb158b96595250cc332901b282d15b0 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/debugfs/file.c | 10 ++++++++++
fs/debugfs/inode.c | 12 ++++++++++++
fs/debugfs/internal.h | 6 ++++++
3 files changed, 28 insertions(+)

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index df5c2162e7297..a1aea4d1637c7 100644
--- 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 5290a721a703f..014ff204548d9 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -219,6 +219,14 @@ 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);
}

@@ -712,6 +720,10 @@ 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 f7c489b5a368c..c7d61cfc97d26 100644
--- 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
};
};
};
--
2.42.0