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author | Steven Rostedt (Google) <rostedt@goodmis.org> | 2022-03-01 22:29:04 -0500 |
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committer | Steven Rostedt (Google) <rostedt@goodmis.org> | 2022-03-01 22:48:30 -0500 |
commit | 1d1898f65616c4601208963c3376c1d828cbf2c7 (patch) | |
tree | 80b78cfcea04fedc610f7ad2efee28d660088f92 /kernel/trace/trace_events_hist.c | |
parent | 90f59ee41abf587ad4675a70434136c8707fdf4b (diff) | |
download | linux-stable-1d1898f65616c4601208963c3376c1d828cbf2c7.tar.gz linux-stable-1d1898f65616c4601208963c3376c1d828cbf2c7.tar.bz2 linux-stable-1d1898f65616c4601208963c3376c1d828cbf2c7.zip |
tracing/histogram: Fix sorting on old "cpu" value
When trying to add a histogram against an event with the "cpu" field, it
was impossible due to "cpu" being a keyword to key off of the running CPU.
So to fix this, it was changed to "common_cpu" to match the other generic
fields (like "common_pid"). But since some scripts used "cpu" for keying
off of the CPU (for events that did not have "cpu" as a field, which is
most of them), a backward compatibility trick was added such that if "cpu"
was used as a key, and the event did not have "cpu" as a field name, then
it would fallback and switch over to "common_cpu".
This fix has a couple of subtle bugs. One was that when switching over to
"common_cpu", it did not change the field name, it just set a flag. But
the code still found a "cpu" field. The "cpu" field is used for filtering
and is returned when the event does not have a "cpu" field.
This was found by:
# cd /sys/kernel/tracing
# echo hist:key=cpu,pid:sort=cpu > events/sched/sched_wakeup/trigger
# cat events/sched/sched_wakeup/hist
Which showed the histogram unsorted:
{ cpu: 19, pid: 1175 } hitcount: 1
{ cpu: 6, pid: 239 } hitcount: 2
{ cpu: 23, pid: 1186 } hitcount: 14
{ cpu: 12, pid: 249 } hitcount: 2
{ cpu: 3, pid: 994 } hitcount: 5
Instead of hard coding the "cpu" checks, take advantage of the fact that
trace_event_field_field() returns a special field for "cpu" and "CPU" if
the event does not have "cpu" as a field. This special field has the
"filter_type" of "FILTER_CPU". Check that to test if the returned field is
of the CPU type instead of doing the string compare.
Also, fix the sorting bug by testing for the hist_field flag of
HIST_FIELD_FL_CPU when setting up the sort routine. Otherwise it will use
the special CPU field to know what compare routine to use, and since that
special field does not have a size, it returns tracing_map_cmp_none.
Cc: stable@vger.kernel.org
Fixes: 1e3bac71c505 ("tracing/histogram: Rename "cpu" to "common_cpu"")
Reported-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace/trace_events_hist.c')
-rw-r--r-- | kernel/trace/trace_events_hist.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c index ada87bfb5bb8..dc7f733b4cb3 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -2289,9 +2289,9 @@ parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file, /* * For backward compatibility, if field_name * was "cpu", then we treat this the same as - * common_cpu. + * common_cpu. This also works for "CPU". */ - if (strcmp(field_name, "cpu") == 0) { + if (field && field->filter_type == FILTER_CPU) { *flags |= HIST_FIELD_FL_CPU; } else { hist_err(tr, HIST_ERR_FIELD_NOT_FOUND, @@ -4832,7 +4832,7 @@ static int create_tracing_map_fields(struct hist_trigger_data *hist_data) if (hist_field->flags & HIST_FIELD_FL_STACKTRACE) cmp_fn = tracing_map_cmp_none; - else if (!field) + else if (!field || hist_field->flags & HIST_FIELD_FL_CPU) cmp_fn = tracing_map_cmp_num(hist_field->size, hist_field->is_signed); else if (is_string_field(field)) |