Messages in this thread | | | Date | Wed, 10 Nov 2021 08:03:04 +0100 | From | Greg Kroah-Hartman <> | Subject | Re: [PATCH 2/2] kobject: wait until kobject is cleaned up before freeing module |
| |
On Wed, Nov 10, 2021 at 09:20:27AM +0800, Ming Lei wrote: > On Tue, Nov 09, 2021 at 02:14:09PM +0100, Petr Mladek wrote: > > On Tue 2021-11-09 10:00:27, Ming Lei wrote: > > > On Mon, Nov 08, 2021 at 06:26:25PM +0100, Petr Mladek wrote: > > > > On Fri 2021-11-05 14:37:10, Ming Lei wrote: > > > > > kobject_put() may become asynchronously because of > > > > > CONFIG_DEBUG_KOBJECT_RELEASE, so once kobject_put() returns, the caller may > > > > > expect the kobject is released after the last refcnt is dropped, however > > > > > CONFIG_DEBUG_KOBJECT_RELEASE just schedules one delayed work function > > > > > for cleaning up the kobject. Inside the cleanup handler, kobj->ktype and > > > > > kobj->ktype->release are required. > > > > > > > > > > It is supposed that no activity is on kobject itself any more since > > > > > module_exit() is started, so it is reasonable for the kobject user or > > > > > driver to expect that kobject can be really released in the last run of > > > > > kobject_put() in module_exit() code path. Otherwise, it can be thought as > > > > > one driver's bug since the module is going away. > > > > > > > > Honestly, this looks a bit fragile. What if there is still another > > > > reference from some reason. IMHO, it is easy to do it wrong. > > > > The kobject stuff is super-tricky. > > > > > > > > Yes, there is the argument that it is a drivers bug when it does not > > > > work. > > > > > > That is another 'issue'(even not sure if there is really), and it isn't covered > > > in this patchset, which focuses on fixing CONFIG_DEBUG_KOBJECT_RELEASE, so > > > please do not mix the two here. > > > > Yes, it is another issue but the relation is very important. > > > > My understanding is that this patch prevents problems caused by > > the delayed work. The kobject is added into kobj_cleanup_list > > only when the delayed work is scheduled. The patch has no effect > > if the delayed work is not used. > > > > From my POV, this patch kind of removes the effect of the delayed > > work. My point is: > > > > Does it still make sense to use the delayed work in the first place? > > Will the delayed work still help to catch some problems? > > That depends on the user of CONFIG_DEBUG_KOBJECT_RELEASE, if users > thought it is useless, I think it is fine to remove it. > > Greg, any idea about if CONFIG_DEBUG_KOBJECT_RELEASE is useful now?
Yes it is, it finds driver bugs where they do things wrong.
I've been ignoring this thread until after 5.16-rc1 is out, sorry.
greg k-h
| |