On 12/04/2018 02:08 PM, Bart Van Assche wrote: > On Tue, 2018-12-04 at 13:57 -0500, Waiman Long wrote: >> On 12/03/2018 07:28 PM, Bart Van Assche wrote: >>> The next patch in this series uses the class name in code that >>> detects lock class use-after-free. Hence retain the class name for >>> lock classes that are being freed. >>> >>> Cc: Peter Zijlstra <[email protected]> >>> Cc: Waiman Long <[email protected]> >>> Cc: Johannes Berg <[email protected]> >>> Signed-off-by: Bart Van Assche <[email protected]> >>> --- >>> kernel/locking/lockdep.c | 4 +--- >>> 1 file changed, 1 insertion(+), 3 deletions(-) >>> >>> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c >>> index ecd92969674c..92bdb187987f 100644 >>> --- a/kernel/locking/lockdep.c >>> +++ b/kernel/locking/lockdep.c >>> @@ -4147,10 +4147,8 @@ static void zap_class(struct lock_class *class) >>> * Unhash the class and remove it from the all_lock_classes list: >>> */ >>> hlist_del_rcu(&class->hash_entry); >>> + class->hash_entry.pprev = NULL; >>> list_del(&class->lock_entry); >>> -page >>> - RCU_INIT_POINTER(class->key, NULL); >>> - RCU_INIT_POINTER(class->name, NULL); >>> } >>> >>> static inline int within(const void *addr, void *start, unsigned long size) >> Using the name after module unload can be problematic if it points to >> memory space occupied by the unloaded kernel module. The memory page may >> be invalid with the potential of crashing the kernel. You may have to >> duplicate the name if it is really from the module address space. > The class name shouldn't be used by any of the code I introduced in the > lockdep infrastructure after unloading a kernel module finished unless if > some of the kernel module code is still running after unloading the kernel > module finished. I think if that happens that the kernel module author is > to blame and not lockdep :-) > > Bart.
You do use the name once in a WARN_ON check in check_prev_add(). You commit log did say the class name will be used. -Longman
