From: Michal Koutný <mkoutny@suse.com>
Date: Wed, 24 Sep 2025 11:38:09 +0000 (+0200)
Subject: tracing: Ensure optimized hashing works
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=2378a191f440a06e4c60fb8a50f4cb708c10ba40;p=users%2Fhch%2Fmisc.git

tracing: Ensure optimized hashing works

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

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.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@suse.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---

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);
 
 	/*