From mboxrd@z Thu Jan 1 00:00:00 1970 From: linux@arm.linux.org.uk (Russell King - ARM Linux) Date: Sat, 25 Jul 2015 15:42:29 +0100 Subject: [PATCH 1/3] nmi: create generic NMI backtrace implementation In-Reply-To: <55A77E9D.2030509@linaro.org> References: <20150715203911.GF7557@n2100.arm.linux.org.uk> <55A7753C.9020708@linaro.org> <20150716093744.GI7557@n2100.arm.linux.org.uk> <55A77E9D.2030509@linaro.org> Message-ID: <20150725144229.GZ7557@n2100.arm.linux.org.uk> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Jul 16, 2015 at 10:51:25AM +0100, Daniel Thompson wrote: > On 16/07/15 10:37, Russell King - ARM Linux wrote: > >That can be implemented in the arch raise() method if needed - most > >architectures shouldn't need it as if they are properly raising a NMI > >which is, by definition, deliverable with normal IRQs disabled. > > Agreed. The bug certainly could be fixed in the ARM raise() function. > > However I'm still curious whether there is any architecture that benefits > from forcing the current CPU into an NMI handler? Why doesn't the > don't-run-unnecessary-code argument apply here as well? The benefit is that we get a consistent way of invoking the backtrace, since causing the NMI exception gives us a 'struct pt_regs' to work with, which we wouldn't otherwise have if we tried to call it "inline". The NMI backtrace includes dumping the register state of the NMI- receiving CPUs, which needs a 'struct pt_regs' and generating a that in arch-independent code wouldn't be nice. In any case, if this area needs changing in the generic code, it should be done as a separate change so that it can be properly assessed and validated on x86. In the mean time, I will action Thomas' request to put it into my tree so that we can get some reasonable linux-next time with it, and hopefully have some progress towards FIQ-based backtracing for ARM. Thanks. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net.