linux-kernel - [PATCH v6 12/12] kernel/kthread: show a warning if kthread's comm is truncated

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Message-Id: <20211025083315.4752-13-laoar.shao@gmail.com>
Date:   Mon, 25 Oct 2021 08:33:15 +0000
From:   Yafang Shao <laoar.shao@...il.com>
To:     akpm@...ux-foundation.org, keescook@...omium.org,
        rostedt@...dmis.org, mathieu.desnoyers@...icios.com,
        arnaldo.melo@...il.com, pmladek@...e.com, peterz@...radead.org,
        viro@...iv.linux.org.uk, valentin.schneider@....com,
        qiang.zhang@...driver.com, robdclark@...omium.org,
        christian@...uner.io, dietmar.eggemann@....com, mingo@...hat.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        davem@...emloft.net, kuba@...nel.org, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, kafai@...com,
        songliubraving@...com, yhs@...com, john.fastabend@...il.com,
        kpsingh@...nel.org, dennis.dalessandro@...nelisnetworks.com,
        mike.marciniszyn@...nelisnetworks.com, dledford@...hat.com,
        jgg@...pe.ca
Cc:     linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, oliver.sang@...el.com, lkp@...el.com,
        Yafang Shao <laoar.shao@...il.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>
Subject: [PATCH v6 12/12] kernel/kthread: show a warning if kthread's comm is truncated

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

truncated kthread comm:I-am-a-kthread-with-lon, pid:14 by 6 characters

Suggested-by: Petr Mladek <pmladek@...e.com>
Signed-off-by: Yafang Shao <laoar.shao@...il.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Kees Cook <keescook@...omium.org>
Cc: Petr Mladek <pmladek@...e.com>
---
 kernel/kthread.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 5b37a8567168..46b924c92078 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.
-- 
2.17.1