On Tue, Oct 26, 2021 at 11:37:30PM +0800, Ming Lei wrote:

On Tue, Oct 26, 2021 at 10:48:18AM +0200, Petr Mladek wrote:

quoted

Livepatch code never called kobject_del() under a lock. It would cause
the obvious deadlock.

Never?

quoted

The historic code only waited in the
module_exit() callback until the sysfs interface was removed.

OK, then Luis shouldn't consider livepatching as one such issue to solve
with one generic solution.

It's not what I was told when the deadlock was found with zram, so I was
informed quite the contrary.

I'm working on a generic coccinelle patch which hunts for actual cases
using iteration (a feature of coccinelle for complex searches). The
search is pretty involved, so I don't think I'll have an answer to this
soon.

Since the question of how generic this deadlock is remains questionable,
I think it makes sense to put the generic deadlock fix off the table for
now, and we address this once we have a more concrete search with
coccinelle.

But to say we *don't* have drivers which can cause this is obviously
wrong as well, from a cursory search so far. But let's wait and see how
big this list actually is.

I'll drop the deadlock generic fixes and move on with at least a starter
kernfs / sysfs tests.

  Luis