linux-kernel - [for-next][PATCH 10/11] tracing: Ensure optimized hashing works

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Message-ID: <20250930170302.878862549@kernel.org>
Date: Tue, 30 Sep 2025 13:01:45 -0400
From: Steven Rostedt <rostedt@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Michal Koutný <mkoutny@...e.com>
Subject: [for-next][PATCH 10/11] tracing: Ensure optimized hashing works

From: =?UTF-8?q?Michal=20Koutn=C3=BD?= <mkoutny@...e.com>

If ever PID_MAX_DEFAULT changes, it must be compatible with tracing
hashmaps assumptions.

Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Link: https://lore.kernel.org/20250924113810.2433478-1-mkoutny@suse.com
Link: https://lore.kernel.org/r/20240409110126.651e94cb@gandalf.local.home/
Signed-off-by: Michal Koutný <mkoutny@...e.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 kernel/trace/trace_sched_switch.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/trace/trace_sched_switch.c b/kernel/trace/trace_sched_switch.c
index 518dfc74347a..c46d584ded3b 100644
--- a/kernel/trace/trace_sched_switch.c
+++ b/kernel/trace/trace_sched_switch.c
@@ -247,6 +247,8 @@ int trace_save_cmdline(struct task_struct *tsk)
 	if (!tsk->pid)
 		return 1;
 
+	BUILD_BUG_ON(!is_power_of_2(PID_MAX_DEFAULT));
+
 	tpid = tsk->pid & (PID_MAX_DEFAULT - 1);
 
 	/*
-- 
2.50.1