On Mon, Sep 28, 2020 at 05:22:33PM -0500, Kim Phillips wrote: > On 5/19/20 2:52 PM, tip-bot2 for Thomas Gleixner wrote: > > The following commit has been merged into the core/rcu branch of tip: > > > > Commit-ID: ff5c4f5cad33061b07c3fb9187506783c0f3cb66 > > Gitweb: https://git.kernel.org/tip/ff5c4f5cad33061b07c3fb9187506783c0f3cb66 > > Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > AuthorDate: Fri, 13 Mar 2020 17:32:17 +01:00 > > Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > CommitterDate: Tue, 19 May 2020 15:51:20 +02:00 > > > > rcu/tree: Mark the idle relevant functions noinstr > > > > These functions are invoked from context tracking and other places in the > > low level entry code. Move them into the .noinstr.text section to exclude > > them from instrumentation. > > > > Mark the places which are safe to invoke traceable functions with > > instrumentation_begin/end() so objtool won't complain. > > > > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > Reviewed-by: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx> > > Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > > Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > Link: https://lkml.kernel.org/r/20200505134100.575356107@xxxxxxxxxxxxx > > > > > > --- > > I bisected a system hang condition down to this commit. That's odd, mostly its the lack of noinstr that causes hangs, I've never yet seen the presence of it cause problems. > To reproduce the hang, compile the below code and execute it as root > on an x86_64 server (AMD or Intel). The code is opening a > PERF_TYPE_TRACEPOINT event with a non-zero pe.config. In my experience, it is very relevant which exact tracepoint you end up using. PERF_COUNT_HW_INSTRUCTIONS is a very long and tedious way of writing 1 in this case, on my randonly selected test box this morning, trace event 1 is: $ for file in /debug/tracing/events/*/*/id ; do echo $file -- $(cat $file); done | grep " 1$" /debug/tracing/events/ftrace/function/id -- 1 > If I revert the commit from Linus' ToT, the system stays up. > memset(&pe, 0, sizeof(struct perf_event_attr)); > pe.type = PERF_TYPE_TRACEPOINT; > pe.size = sizeof(struct perf_event_attr); > pe.config = PERF_COUNT_HW_INSTRUCTIONS; > pe.disabled = 1; Doubly funny for not actually enabling the event... > pe.exclude_kernel = 1; > pe.exclude_hv = 1; Still, it seems to make my machine unhappy.. Let's see if I can get anything useful out of it.
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