Re: lock-up with module: Optimize __module_address() using a latched RB-tree

[Peter Zijlstra <peterz@infradead.org>]

On Tue, Jul 07, 2015 at 11:56:20PM +0200, Peter Zijlstra wrote:
> On Wed, Jul 08, 2015 at 05:45:45AM +0930, Arthur Marsh wrote:
> > I'm not aware of any modules being loaded with --force .
> > 
> > I've applied the patch, thanks!
> > 
> > The resultant kernel locked up as follows:
> > 
> > http://www.users.on.net/~arthur.marsh/20150708469.jpg
> 
> This has "Not tainted" which would indeed rule out forced loading. So
> much for that idea :/
> 
> > http://www.users.on.net/~arthur.marsh/20150708470.jpg
> 
> And that one has a bunch of NMI prints, curious those. But given Mathieu
> made them return NULL, that completely rules out the most interesting
> races.

Could you try the below? It appears there was a spot freeing modules
that forgot to take them out of the tree.

If that fails, try and disable CONFIG_MODULE_UNLOAD.

---
 kernel/module.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/module.c b/kernel/module.c
index 3e0e19763d24..4d2b82e610e2 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3557,6 +3557,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
 	mutex_lock(&module_mutex);
 	/* Unlink carefully: kallsyms could be walking list. */
 	list_del_rcu(&mod->list);
+	mod_tree_remove(mod);
 	wake_up_all(&module_wq);
 	/* Wait for RCU-sched synchronizing before releasing mod->list. */
 	synchronize_sched();