linux-kernel - [PATCH v2] tracing: Ensure optimized hashing works

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Message-ID: <20250924113810.2433478-1-mkoutny@suse.com>
Date: Wed, 24 Sep 2025 13:38:09 +0200
From: Michal Koutný <mkoutny@...e.com>
To: linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org
Cc: Michal Koutný <mkoutny@...e.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [PATCH v2] tracing: Ensure optimized hashing works

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

Link: https://lore.kernel.org/r/20240409110126.651e94cb@gandalf.local.home/
Signed-off-by: Michal Koutný <mkoutny@...e.com>
---
 kernel/trace/trace_sched_switch.c | 2 ++
 1 file changed, 2 insertions(+)

v1 in https://lore.kernel.org/r/20250923165908.2399256-1-mkoutny@suse.com/
- cohere with code (Steven)

diff --git a/kernel/trace/trace_sched_switch.c b/kernel/trace/trace_sched_switch.c
index cb49f7279dc80..9ee62364d98d2 100644
--- a/kernel/trace/trace_sched_switch.c
+++ b/kernel/trace/trace_sched_switch.c
@@ -248,6 +248,8 @@ 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);
 
 	/*
-- 
2.51.0