On Thu, May 16, 2019 at 11:51:55PM +0000, Song Liu wrote: > Hi, > > We found a failure with selftests/bpf/tests_prog in test_stacktrace_map (on > bpf/master > branch). > > After digging into the code, we found that perf_callchain_kernel() is giving > empty > callchain for tracepoint sched/sched_switch. And it seems related to commit > > d15d356887e770c5f2dcf963b52c7cb510c9e42d > ("perf/x86: Make perf callchains work without CONFIG_FRAME_POINTER") > > Before this commit, perf_callchain_kernel() returns callchain with regs->ip. > With > this commit, regs->ip is not sent for !perf_hw_regs(regs) case.
So while I think the below is indeed right; we should store regs->ip regardless of the unwind path chosen, I still think there's something fishy if this results in just the 1 entry. The sched/sched_switch event really should have a non-trivial stack. Let me see if I can reproduce with just perf.