Re: kobject: provide kobject_put_wait to fix module unload race

From: Mike Snitzer
Date: Tue Jan 07 2014 - 18:19:30 EST

On Tue, Jan 07 2014 at 3:16pm -0500,
Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:

> On Tue, 7 Jan 2014, Mike Snitzer wrote:
> > I've staged your patch in linux-next for 3.14, see:
> >
> Looking at this patch, I realize that it is buggy too. If module unload
> happens at this point (after the completion is signaled, but before the
> release function returns), it crashes.
> static void dm_kobject_release(struct kobject *kobj)
> {
> complete(dm_get_completion_from_kobject(kobj));
> >========== module unload here ===============<
> }

That race isn't a surprise, thought you pointed it out earlier in this
thread? Anyway, I'm inclined to keep the racey patch staged in
linux-dm.git until the stalemate with gregkh is resolved. DM is no
worse than other code that follows this same wait for completion

> The patch that I sent initially in this thread doesn't have this bug
> because the completion is signaled in non-module code.
> That goes back to my initial claim - it is impossible to use the kobject
> interface correctly! But if Greg doesn't want a patch that fixes the
> kobject interface, I don't really know what to do about it.

Right, I'm missing what is wrong with your proposed kobject_put_wait

Greg, can you please establish that you understand the problem, and
existing kobject patterns, before you dismiss a fix?
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at