tracing: Let histogram values keep the percent and graph modifiers

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The .percent and .graph modifiers exist only for histogram values, but a
value carrying either of them has been rejected since v6.3. The example
in Documentation/trace/histogram.rst,

  # echo 'hist:keys=prev_comm:vals=hitcount.percent:nohitcount' > \
	 events/sched/sched_switch/trigger

returns -EINVAL.

parse_field() sets the two flags only when the field is neither a key nor
a variable, that is, only on a value:

	} else if (strncmp(modifier, "percent", 7) == 0) {
		if (*flags & (HIST_FIELD_FL_VAR | HIST_FIELD_FL_KEY))
			goto error;
		*flags |= HIST_FIELD_FL_PERCENT;

__create_val_field() then rejects a value for carrying them, so no field
can reach hist_trigger_print_val(), where both are implemented.

commit e0213434fe ("tracing: Do not let histogram values have some
modifiers") added the check after a value with .buckets oopsed in
hist_field_name(). That happens because .buckets and .log2 make
create_hist_field() build a nested field in operands[0] which
hist_field_name() then walks into. The percent and graph flags do not
create an operand and are not read by hist_field_name(); they are only
used when printing a value.

Stop rejecting the two flags on a value. The check for variables is left
alone, where they are unreachable anyway because parse_field() rejects a
variable carrying them first.

With the two flags removed, the trigger above installs and prints as
documented:

  { prev_comm: rcu_preempt  }  hitcount (%):   0.00
  { prev_comm: init         }  hitcount (%):  99.98
  Totals:
      Hits: 237896

Cc: stable@vger.kernel.org
Fixes: e0213434fe ("tracing: Do not let histogram values have some modifiers")
Link: https://patch.msgid.link/20260907052113.430818-1-donggeunyoo.kernel@gmail.com
Signed-off-by: Donggeun Yoo <donggeunyoo.kernel@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

...

This commit is contained in:

Donggeun Yoo 2026-09-07 14:21:13 +09:00 • committed by Steven Rostedt

parent 06f5634ec5

commit 3d617bfd79

1 changed files with 1 additions and 2 deletions

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kernel/trace/trace_events_hist.c

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