A hist trigger with an onmatch() action copies the key list of the compatible histogram it finds on the matched event. Reading each key's name straight out of key_field->field->name faults on any pseudo-field key. 2/2 renders the key with expr_field_str() instead; 1/2 teaches that renderer to emit a bucket count, which 2/2 needs before it can use it.
Link: https://lore.kernel.org/linux-trace-kernel/[email protected]/ Changes since v1: - Split the single patch in two. - Dropped the third change, which gated the ".stacktrace" arm of get_hist_field_flags() on hist_field->field. It fixes nothing: hist_field_print() excludes FL_STACKTRACE before it ever calls get_hist_field_flags(), and parse_field() takes the "stacktrace" modifier on any field. Measured with and without it: identical generated command on all nine key kinds below. - 1/2 is not separable from 2/2. .buckets is refused on a value, so no expression can reach expr_field_str() with a bucketed field, and 2/2 alone turns a working .buckets key into a refused one. In this order no bisection point regresses. The command create_field_var_hist() generates, for each kind of key the copied histogram can carry: WK key unpatched patched pid keys=pid keys=pid pid.log2 keys=pid keys=pid.log2 pid.buckets=10 keys=pid keys=pid.buckets=10 common_cpu oops keys=common_cpu common_comm oops keys=common_comm common_timestamp oops keys=common_timestamp common_timestamp.usecs oops keys=common_timestamp.usecs common_stacktrace oops keys=common_stacktrace.stacktrace hitcount oops keys=hitcount x86_64 under QEMU, CONFIG_KASAN=y, 4 CPUs, base 2f0c1cf72f46. A compatible histogram on sched_waking keyed on WK, an onmatch() target on sched_switch keyed on SK, my_synth($wakeup_lat,prio) forcing a field variable. Donggeun Yoo (2): tracing: Add the bucket size to expr_field_str() tracing: Fix NULL dereference when copying keys for a field variable kernel/trace/trace_events_hist.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) -- 2.53.0
