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Sun, 13 Sep 2026 13:31:39 -0700 (PDT) From: Donggeun Yoo To: Steven Rostedt , Masami Hiramatsu Cc: Mathieu Desnoyers , Tom Zanussi , linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, Donggeun Yoo , stable@vger.kernel.org Subject: [PATCH v2 1/2] tracing: Add the bucket size to expr_field_str() Date: Mon, 14 Sep 2026 05:31:28 +0900 Message-ID: <20260913203129.941270-2-donggeunyoo.kernel@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260913203129.941270-1-donggeunyoo.kernel@gmail.com> References: <20260913203129.941270-1-donggeunyoo.kernel@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" expr_field_str() renders a HIST_FIELD_FL_BUCKET field as "pid.buckets", dropping the count, and parse_field() rejects that spelling. get_hist_field_flags() returns the bare string "buckets" and keeps the count in hist_field->buckets. hist_field_print() appends it, expr_field_str() never did. Nothing reaches it today, since .buckets is refused on a value and no expression can carry one, but the next patch renders histogram keys with expr_field_str(), where a .buckets key is legal. Append the count, as hist_field_print() does. Cc: stable@vger.kernel.org Fixes: de9a48a360b7 ("tracing: Add linear buckets to histogram logic") Signed-off-by: Donggeun Yoo Assisted-by: Claude:claude-fable-5 --- kernel/trace/trace_events_hist.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_h= ist.c index 963e0d6b61fd..9d7ce01fda36 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -1755,6 +1755,9 @@ static bool expr_field_str(struct hist_field *field, = struct seq_buf *s) seq_buf_printf(s, ".%s", flags_str); } =20 + if (field->buckets) + seq_buf_printf(s, "=3D%ld", field->buckets); + return !seq_buf_has_overflowed(s); } =20 --=20 2.53.0 From nobody Fri Sep 25 11:05:14 2026 Received: from mail-pj2-f12.google.com (mail-pj2-f12.google.com [74.125.227.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B6F352F0661 for ; Sun, 13 Sep 2026 20:31:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; 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charset="utf-8" In event_hist_trigger_parse() where it needs to create actions like "onmatch", it calls: event_hist_trigger_parse() { create_actions() { action_create() { trace_action_create() { trace_action_create_field_var() { create_field_var_hist() Where create_field_var_hist() does a loop on the hist_data representing the keys. The issue is, if the keys uses one of the pseudo field types (like common_cpu), the hist_data field element will have NULL for its field member causing a NULL pointer dereference when accessing the key_field->field->name. # echo 'hist:keys=3Dcommon_cpu:ts0=3Dcommon_timestamp.usecs' > \ events/sched/sched_waking/trigger # echo 'my_synth u64 lat; int prio' > synthetic_events # echo 'hist:keys=3Dcommon_cpu:wakeup_lat=3Dcommon_timestamp.usecs-$ts0:\ onmatch(sched.sched_waking).my_synth($wakeup_lat,prio)' > \ events/sched/sched_switch/trigger KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017] RIP: 0010:create_field_var_hist+0x771/0x1380 Call Trace: trace_action_create_field_var+0x360/0x600 trace_action_create+0x393/0xe80 event_hist_trigger_parse+0x3e47/0x69e0 trigger_process_regex+0x1a6/0x250 event_trigger_write+0xce/0x160 Instead of accessing it directly, use the proper handler expr_field_str() to get the name. A .buckets key needs the previous patch to render, so apply that first. Cc: stable@vger.kernel.org Fixes: 02205a6752f2 ("tracing: Add support for 'field variables'") Signed-off-by: Donggeun Yoo Assisted-by: Claude:claude-fable-5 --- kernel/trace/trace_events_hist.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_h= ist.c index 9d7ce01fda36..b43b83d7c6f3 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -3097,7 +3097,7 @@ create_field_var_hist(struct hist_trigger_data *targe= t_hist_data, key_field =3D hist_data->fields[i]; if (!first) seq_buf_putc(&s, ','); - seq_buf_puts(&s, key_field->field->name); + expr_field_str(key_field, &s); first =3D false; } =20 --=20 2.53.0