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:
> > http://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=for-next&id=af7b1e5c767fc895788c971c8f4686402ac8344f
> 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)
> >========== 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?
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