On Tue, 25 Jun 2024 08:20:15 -0500 Andrew Halaney <ahalaney@xxxxxxxxxx> wrote: > So I ended up doing a sequence like: > > tracing_off(); > ftrace_dump(DUMP_ALL); I've done that several times too. > > in the softlockup code when it was detected. Ideally I wanted to look at > the vmcore and look at the ftrace data in there (since debugging printk > by using printk is a little confusing), but there was a makedumpfile bug > I hit... so I went with the hacky route to prove to myself what was > going on. I think since then that's been resolved. Hope that helps! You may be interested in some work I'm doing that allows you to read the ring buffer from a previous kernel after a crash. https://lore.kernel.org/linux-trace-kernel/20240612231934.608252486@xxxxxxxxxxx/ I also have a way to ask for any memory, that should be able to get the same location most times, via a "reserve_mem=" kernel command line parameter. https://lore.kernel.org/linux-trace-kernel/20240613233415.734483785@xxxxxxxxxxx/ They are both destined for the next merge window. After that, I have one more patch that ties the two together, so that you can have a kernel command line of: reserve_mem=12M:4096:trace trace_instance=bootmap@trace and then when you boot up, you would have a trace instance that would be mapped to that memory. If your machine doesn't clear memory after a crash, you can read the data from the crash on the next boot. -- Steve
