On Fri 2018-09-07 09:45:31, Peter Zijlstra wrote: > On Thu, Sep 06, 2018 at 11:31:51AM +0900, Sergey Senozhatsky wrote: > > An alternative option, thus, could be re-instating back the rule that > > lockdep_off/on should be the first and the last thing we do in > > nmi_enter/nmi_exit. E.g. > > > > nmi_enter() > > lockdep_off(); > > printk_nmi_enter(); > > > > nmi_exit() > > printk_nmi_exit(); > > lockdep_on(); > > Yes that. Also, those should probably be inline functions. > > --- > Subject: locking/lockdep: Fix NMI handling > > Someone put code in the NMI handler before lockdep_off(). Since lockdep > is not NMI safe, this wrecks stuff.
My view is that nmi_enter() has to switch several features into NMI-safe mode. The code must not trigger the other features when they are still in the unsafe mode. It is a chicken&egg problem. And it is hard to completely prevent regressions caused by future changes. I though that printk_nmi_enter() should never need any lockdep-related code. On the other hand, people might want to printk debug messages when lockdep_off() is called. This is why I put it in the current order. That said, I am not against this change. Especially the inlining is a good move. Note that lockdep_off()/lockdep_on() must not be traced as well. Best Regards, Petr
