On Wed, 29 Jun 2016 09:57:41 +0900 Minchan Kim <minchan@xxxxxxxxxx> wrote: > Hello, > > On Tue, Jun 28, 2016 at 06:46:34PM +0200, Rabin Vincent wrote: > > On Tue, Jun 28, 2016 at 03:33:18PM +0900, Namhyung Kim wrote: > > > On Tue, Jun 28, 2016 at 3:25 PM, Namhyung Kim <namhyung@xxxxxxxxxx> wrote: > > > > I'm running some guest machines for kernel development. For debugging > > > > purpose, I use lots of trace_printk() since it's faster than normal > > > > printk(). When kernel crash happens the trace buffer is printed on > > > > console (I set ftrace_dump_on_oops) but it takes too much time. I > > > > don't want to reduce the size of ring buffer as I want to collect the > > > > debug info as much as possible. And I also want to see trace from all > > > > cpu so 'ftrace_dump_on_oop = 2' is not an option. > > > > > > > > I know the kexec/kdump (and the crash tool) can dump and analyze the > > > > trace buffer later. But it's cumbersome to do it everytime and more > > > > importantly, I don't want to spend the memory for the crashkernel. > > > > Assuming you're using QEMU: > > > > QEMU has a dump-guest-memory command which can be used to dump the > > guest's entire memory to an ELF which can be loaded by the crash utility > > to extract the trace buffer. This doesn't require kexec/kdump or any > > other support from the guest kernel. > > Thanks for the hint. It's surely handy rather than kexec/kdump. > > A question is that it's possible to capture guest's entire memory > when guest kernel is oops? > I mean I don't want to capture alive guest but get snapshot image > when guest kernel encounters BUG_ON and see event trace from the > image. > > Anyway, I tried crashtool and load trace.so but failed to load > extension module 'trace.so' because read_string failed in > ftrace_get_event_type_name of trace.c. > Does it work with recent kernel? > > My kernel is 4.7.0-rc4-mm1. It probably needs another update. I usually send patches to David Anderson for updates. Fujitsu started that work and was maintaining it for a while, but I don't think they are anymore. I have no problem maintaining the trace.so module. If I get time tomorrow, I'll see if I can get it up to date again. -- Steve > > > > > It's apparently even possible to run QEMU with the guest memory in a > > file and load that to crash directly, although this is not something > > I've had a chance to try out myself: > > > > https://github.com/crash-utility/crash/commit/89ed9d0a7f7da4578294a492c1ad857244ce7352 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
