Re: [PATCH] livepatch: fix race between enabled_store() and klp_unregister_patch()

Josh Poimboeuf
2015-12-01T15:53:41Z

On Tue, Dec 01, 2015 at 09:50:23AM +0100, Jiri Slaby wrote:
> On 12/01/2015, 02:11 AM, Josh Poimboeuf wrote:
> > When I try to recreate something similar by putting a delay in
> > enabled_store(), klp_free_patch() just sleeps on its call to
> > kobject_put() until enabled_store() returns. The unregister stack looks
> > like:
> >
> > [<ffffffff812e966b>] __kernfs_remove+0x1fb/0x380
> > [<ffffffff812ea273>] kernfs_remove+0x23/0x40
> > [<ffffffff812ec601>] sysfs_remove_dir+0x51/0x80
> > [<ffffffff81407fb8>] kobject_del+0x18/0x50
> > [<ffffffff8140804a>] kobject_release+0x5a/0x190
> > [<ffffffff81407f27>] kobject_put+0x27/0x50
>
> What about _put outside of klp_mutex in klp_unregister_patch (and maybe
> the other _put's as well)? Plus Li Bin's patch.

This approach sounds the best to me. I think all _put's for the patch
kobj need to be outside the mutex. There's also a _put for the patch
kobj in the klp_init_patch() error path which needs to be moved out.

I think the rest of the _put's (for object and func kobjs) are fine as
they are, because they don't have corresponding sysfs functions which
get the mutex.

--
Josh