Messages in this thread | | | Date | Mon, 25 Jun 2018 17:28:24 +0900 | From | Byungchul Park <> | Subject | Re: [RFC 2/2] rcu: Remove ->dynticks_nmi_nesting from struct rcu_dynticks |
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On Fri, Jun 22, 2018 at 01:05:48PM -0700, Joel Fernandes wrote: > On Fri, Jun 22, 2018 at 02:32:47PM -0400, Steven Rostedt wrote: > > On Fri, 22 Jun 2018 11:19:16 -0700 > > Joel Fernandes <joel@joelfernandes.org> wrote: > > > > > Sure. So in a later thread you mentioned "usermode helpers". I took a closer > > > look at that subsystem, and it seems you can execute usermode helpers from > > > atomic sections with help of UMH_NO_WAIT flag. > > > > > > Then I checked where this flag is used and it turns out its from the > > > mce_work_trigger function in x86/kernel/cpu/mcheck/dev-mcelog.c which can be > > > called infact from an interrupt context (mce_notify_irq). > > > > > > Is this the usecase you remember causing this weird transitions to userspace? > > > > But this case still looks like it uses work queues, it just doesn't > > wait for the result. > > > > I'll have to look at the code from what it looked like back in 2011, to > > see if there was an actual issue here back then. > > Good point Steve. So I guess in the current kernel sources, there's no code > that uses UMH in IRQ context AFAICT. I'll go through the google group thread > Paul pointed as well to study the history of the problem a bit more.
Me too. Good discussion we had thanks to you, Joel.
> thanks, > > - Joel
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