[LU-14463] stack traces not being printed to console on RHEL8

Related — Thu, 5 May 2022 13:50:48 +0000

I noticed in a recent test that instead of getting a stack trace printed to the console, all that is shown on the MDS console in the log is:
https://testing.whamcloud.com/test_sets/92361cb8-6cb4-4045-a0df-c9efc31520ea

[  508.376802] Call Trace TBD:
[  508.378011] Pid: 31468, comm: mdt00_033 4.18.0-240.1.1.el8_lustre.x86_64 #1 SMP Fri Feb 19 20:34:57 UTC 2021
[  508.379472] Call Trace TBD:
[  508.379899] Pid: 31454, comm: mdt00_019 4.18.0-240.1.1.el8_lustre.x86_64 #1 SMP Fri Feb 19 20:34:57 UTC 2021
[  508.381521] Call Trace TBD:

which is not very useful. That message comes from patch https://review.whamcloud.com/35239 "LU-12400 libcfs: save_stack_trace_tsk if ARCH_STACKWALK". That patch was ostensibly to fix an issue with 5.4 kernels, but the MDS was running RHEL8.3 (4.18.0-240.1.1.el8_lustre.x86_64).

At a minimum, in libcfs_call_trace() if tsk == current this should fall back to doing something useful:

        spin_lock(&st_lock);
        pr_info("Pid: %d, comm: %.20s %s %s\n", tsk->pid, tsk->comm,
                init_utsname()->release, init_utsname()->version);
        if (task_dump_stack) {
                pr_info("Call Trace:\n");
                nr_entries = task_dump_stack(tsk, entries, MAX_ST_ENTRIES, 0);
                for (i = 0; i < nr_entries; i++)
                        pr_info("[<0>] %pB\n", (void *)entries[i]);
        } else if (tsk == current) {
                dump_stack();
        } else {
                pr_info("can't show stack: kernel doesn't export save_stack_trace_tsk\n");
        }
        spin_unlock(&st_lock);

so that the stack is printed in the common case.

Whamcloud Community JIRA

[LU-14463] stack traces not being printed to console on RHEL8