On Mon, Aug 17, 2020 at 10:42:43AM +0530, Sumit Garg wrote: > On Fri, 14 Aug 2020 at 19:48, Daniel Thompson > <daniel.thompson@xxxxxxxxxx> wrote: > > > > On Fri, Aug 14, 2020 at 05:36:36PM +0530, Sumit Garg wrote: > > > On Thu, 13 Aug 2020 at 15:47, Daniel Thompson > > > <daniel.thompson@xxxxxxxxxx> wrote: > > > > > > > > On Thu, Aug 13, 2020 at 02:55:12PM +0530, Sumit Garg wrote: > > > > > On Thu, 13 Aug 2020 at 05:38, Doug Anderson <dianders@xxxxxxxxxxxx> wrote: > > > > > > On Wed, Aug 12, 2020 at 8:27 AM Doug Anderson <dianders@xxxxxxxxxxxx> wrote: > > > > > > > One > > > > > > > last worry is that I assume that most people testing (and even > > > > > > > automated testing labs) will either always enable NMI or won't enable > > > > > > > NMI. That means that everyone will be only testing one codepath or > > > > > > > the other and (given the complexity) the non-tested codepath will > > > > > > > break. > > > > > > > > > > > > > > > > > The current patch-set only makes this NMI to work when debugger (kgdb) > > > > > is enabled which I think is mostly suitable for development > > > > > environments. So most people testing will involve existing IRQ mode > > > > > only. > > > > > > > > > > However, it's very much possible to make NMI mode as default for a > > > > > particular serial driver if the underlying irqchip supports it but it > > > > > depends if we really see any production level usage of NMI debug > > > > > feature. > > > > > > > > The effect of this patch is not to make kgdb work from NMI it is to make > > > > (some) SysRqs work from NMI. I think that only allowing it to deploy for > > > > kgdb users is a mistake. > > > > > > > > Having it deploy automatically for kgdb users might be OK but it seems > > > > sensible to make this feature available for other users too. > > > > > > I think I wasn't clear enough in my prior reply. Actually I meant to > > > say that this patch-set enables NMI support for a particular serial > > > driver via ".poll_init()" interface and the only current user of that > > > interface is kgdb. > > > > > > So if there are other users interested in this feature, they can use > > > ".poll_init()" interface as well to enable it. > > > > Huh? > > > > We appear to speaking interchangably about users (people who sit in > > front of the machine and want a stack trace) and sub-systems ;-). > > > > I don't think other SysRq commands have quite such a direct relationship > > between the sub-system and the sysrq command. For example who are you > > expecting to call .poll_init() if a user wants to use the SysRq to > > provoke a stack trace? > > > > Ah, I see. So you meant to provide a user-space interface to > dynamically enable/disable NMI debug, correct? It will require IRQ <-> > NMI switching at runtime which should be doable safely. I haven't given much thought to the exact mechanism, though I would perhaps have started by thinking about a module parameter). >From an RFC point of view, I simple think this feature is potentially useful on systems without kgdb (which, let's be honest, are firmly in the majority) so making .poll_init() the only way to activate it is a mistake. Daniel.
