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debugfs: annotate debugfs handlers vs. removal with lockdep

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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>
This commit is contained in:
Johannes Berg 2023-11-24 17:25:25 +01:00
parent 0ed04a1847
commit f4acfcd4de
3 changed files with 28 additions and 0 deletions
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10
fs/debugfs/file.c
View File

@ -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);
}

12
fs/debugfs/inode.c
View File

@ -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);
}

6
fs/debugfs/internal.h
View File

@ -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
};
};
};