[v7,11/11] kernel/kthread: show a warning if kthread's comm is truncated

Commit Message

Yafang Shao Nov. 1, 2021, 6:04 a.m. UTC

Show a warning if task comm is truncated. Below is the result
of my test case:

truncated kthread comm:I-am-a-kthread-with-a-l (pid:178) by 8 characters

As we have extended task comm to 24, all the existing in-tree
kthreads/workqueues are not truncated anymore. So this warning will only
be printed for the newly introduced one if it has a long name.

Suggested-by: Petr Mladek <[e-mail]>
Signed-off-by: Yafang Shao <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Cc: Mathieu Desnoyers <[e-mail]>
Cc: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Alexei Starovoitov <[e-mail]>
Cc: Andrii Nakryiko <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
Cc: Al Viro <[e-mail]>
Cc: Kees Cook <[e-mail]>
Cc: Petr Mladek <[e-mail]>
---
 kernel/kthread.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

Patch

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 5b37a8567168..63f38d3a4f62 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -399,12 +399,17 @@  struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
 	if (!IS_ERR(task)) {
 		static const struct sched_param param = { .sched_priority = 0 };
 		char name[TASK_COMM_LEN];
+		int len;
 
 		/*
 		 * task is already visible to other tasks, so updating
 		 * COMM must be protected.
 		 */
-		vsnprintf(name, sizeof(name), namefmt, args);
+		len = vsnprintf(name, sizeof(name), namefmt, args);
+		if (len >= TASK_COMM_LEN) {
+			pr_warn("truncated kthread comm:%s (pid:%d) by %d characters\n",
+				name, task->pid, len - TASK_COMM_LEN + 1);
+		}
 		set_task_comm(task, name);
 		/*
 		 * root may have changed our (kthreadd's) priority or CPU mask.