On Fri, 15 May 2020 at 22:22, Doug Anderson <diand...@chromium.org> wrote: > > Hi, > > On Fri, May 15, 2020 at 9:36 AM Sergey Senozhatsky > <sergey.senozhat...@gmail.com> wrote: > > > > On (20/05/15 17:32), Sumit Garg wrote: > > > > Can I please have some context what problem does this solve? > > > > > > You can find the problem description here [1] which leads to this fix. > > > > [..] > > > > > [1] https://lkml.org/lkml/2020/5/12/213 > > > > Thanks for the link. I'm slightly surprised it took so many years > > to notice the addition of printk_nmi/printk_safe :)
It's been noticed now since I started playing with NMIs support on arm64 for kgdb. And that's been only possible with the advent of pseudo NMIs on arm64 since Linux 5.3 release. > > I haven't looked at all the details, but IIUC we don't normally enter > kgdb on the primary CPU through a NMI context, but the secondary ones > (on x86) always do. There's a case for the primary CPU to enter kgdb in NMI context too. Consider hard-lockup detection based kernel panic. I guess that's already been working on x86 and should be able to work on arm64 after this patch [1]. [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2020-May/732227.html -Sumit > Most things are run on the primary CPU and I > think it's relatively unlikely for people to change the primary CPU > (though it is possible). > > Probably things got worse when I changed the way "btc" worked to make > it common between all architectures. See commit 9ef50a686b53 > ("UPSTREAM: kdb: Fix stack crawling on 'running' CPUs that aren't the > master"). Though theoretically someone could have changed masters and > reproduced the problem with a simple "bt" before my patch, now a > relatively normal command "btc" would tickle the problem. I didn't > notice it because I work almost totally on arm/arm64 machines and they > don't have NMI (yet). > > In general I've always wondered about why (historically) kgdb bugs > have sometimes gone unnoticed for a period of time. That does seem to > be changing, though, and I've seen a few longstanding bugs getting > fixed recently. :-) > > > -Doug _______________________________________________ Kgdb-bugreport mailing list Kgdb-bugreport@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kgdb-bugreport
