On Tue, 25 Aug 2020 15:30:05 +0200 pet...@infradead.org wrote: > On Tue, Aug 25, 2020 at 10:15:55PM +0900, Masami Hiramatsu wrote: > > > > damn... one last problem is dangling instances.. so close. > > > We can apparently unregister a kretprobe while there's still active > > > kretprobe_instance's out referencing it. > > > > Yeah, kretprobe already provided the per-instance data (as far as > > I know, only systemtap depends on it). We need to provide it for > > such users. > > But if we only have one lock, we can avoid checking NMI because > > we can check the recursion with trylock. It is needed only if the > > kretprobe uses per-instance data. Or we can just pass a dummy > > instance on the stack. > > I think it is true in general, you can unregister a rp while tasks are > preempted.
Would you mean the kretprobe handler (or trampoline handler) will be preempted? All kprobes (including kretprobe) handler is running in non-preemptive state, so it shouldn't happen... > > Anyway,. I think I have a solution, just need to talk to paulmck for a > bit. Ah, you mentioned that the removing the kfree() from the trampline handler? I think we can make an rcu callback which will kfree() the given instances. (If it works in NMI) > > > > Ignoring that issue for the moment, the below seems to actually work. > > > > OK, this looks good to me too. > > I'll make a series to rewrite kretprobe based on this patch, OK? > > Please, I'll send the fix along when I have it. OK, I'm planning to (1) add a generic trampoline code (2) cleanup per-arch trampoline to use generic one, (3) rewrite the generic trampoline to use lockless code. Then it will not break anything. Thank you, -- Masami Hiramatsu <mhira...@kernel.org>
