On Mon, 2019-03-25 at 17:45 +0800, shenghui wrote:
> Sorry to trouble you.
>
> I installed virtualbox-5.2.24 on my system (x86 32) and on bootup I got some
> warning:
> ---------------------
> 1251 [ 42.640869] DEBUG_LOCKS_WARN_ON(!current->hardirqs_enabled)
> 1252 [ 42.640880] WARNING: CPU: 0 PID: 841 at kernel/locking/lockdep.c:4132
> check_flags.part.45+0x9e/0x190
> ...
>
> As no crash afterwards, I just ignore the warning and continue using my
> system.
>
> Later I rmmod some module and run "cat /proc/lockdep", the system crashed.
> (Sorry I cannot capture the crash log as kdump didn't work on my system, but
> I can
> see some words "...normal kernel read fault...")
>
>
> Then I walked through the code and found:
> 1) DEBUG_LOCKS_WARN_ON(!current->hardirqs_enabled) will turn debug_locks to 0
> 2) if !debug_locks, graph_lock() will return 0
> 3) On module unloading, lockdep_free_key_range_reg() will run.
> But when !debug_locks, lockdep_free_key_range_reg() will do nothing.
>
> 4743 static void lockdep_free_key_range_reg(void *start, unsigned long size)
> 4744 {
> ...
> 4751 raw_local_irq_save(flags);
> 4752 locked = graph_lock();
> 4753 if (!locked)
> 4754 goto out_irq;
> ...
> 4759
> 4760 graph_unlock();
> 4761 out_irq:
> 4762 raw_local_irq_restore(flags);
>
> 4) The result is: module is unloaded, but some lock_class related with the
> module
> still exist in all_lock_classes.
> 5) 'cat /proc/lockdep' will access elements of all_lock_classes, and will
> trigger the crash.
>
>
> Seems the usage of "!graph_lock()" can prevent any new changes to
> all_lock_classes and other hashtables
> if !debug_locks.
Hi Shenghui,
None of the rmmod / cat /proc/lockdep tests I ran triggered the above warning.
It would help if you could share the steps you followed to trigger that warning.
Thanks,
Bart.
