Messages in this thread | | | Date | Mon, 13 Jan 2020 12:16:40 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH -tip V2 0/2] kprobes: Fix RCU warning and cleanup |
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On Sat, 11 Jan 2020 21:05:37 -0500 Joel Fernandes <joel@joelfernandes.org> wrote:
> On Sat, Jan 11, 2020 at 08:35:07AM +0900, Masami Hiramatsu wrote: > > Hi Joel and Paul, > > > > On Fri, 10 Jan 2020 16:14:38 -0500 > > Joel Fernandes <joel@joelfernandes.org> wrote: > > > > > On Tue, Jan 07, 2020 at 09:15:35PM +0900, Masami Hiramatsu wrote: > > > > Hello, > > > > > > > > Anyone have any comment on this series? > > > > Without this series, I still see the suspicious RCU warning for kprobe on -tip tree. > > > > > > +Paul since RCU. > > > > > > Hi Masami, > > > > > > I believe I had commented before that I don't agree with this patch: > > > https://lore.kernel.org/lkml/157535318870.16485.6366477974356032624.stgit@devnote2/ > > > > > > The rationale you used is to replace RCU-api with non-RCU api just to avoid > > > warnings. I think a better approach is to use RCU api and pass the optional > > > expression to silence the false-positive warnings by informing the RCU API > > > about the fact that locks are held (similar to what we do for > > > rcu_dereference_protected()). The RCU API will do additional checking > > > (such as making sure preemption is disabled for safe RCU usage etc) as well. > > > > Yes, that is what I did in [1/2] for get_kprobe(). > > Let me clarify the RCU list usage in [2/2]. > > > > With the careful check, other list traversals never be done in non-sleepable > > context, those are always runs with kprobe_mutex held. > > If I correctly understand the Documentation/RCU/listRCU.rst, we should/can use > > non-RCU api for those cases, or do I miss something? > > Yes, that is fine. However personally I prefer not to mix usage of > list_for_each_entry_rcu() and list_for_each_entry() on the same pointer > (kprobe_table). I think it is more confusing and error prone. Just use > list_for_each_entry_rcu() everywhere and pass the appropriate lockdep > expression, instead of calling lockdep_assert_held() independently. Is this > not doable?
Hmm, but isn't it more confusing that user just take a mutex but no rcu_read_lock() with list_for_each_entry_rcu()? In that case, sometimes it might sleep inside list_for_each_entry_rcu(), I thought that might be more confusing mind model for users...
Anyway, if so, please update Documentation/RCU/listRCU.rst too.
Thank you,
-- Masami Hiramatsu <mhiramat@kernel.org>
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