Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Yafang Shao <laoar.shao@gmail.com>
To:     keescook@chromium.org, rostedt@goodmis.org, peterz@infradead.org,
        pmladek@suse.com, viro@zeniv.linux.org.uk,
        akpm@linux-foundation.org, valentin.schneider@arm.com,
        mathieu.desnoyers@efficios.com, qiang.zhang@windriver.com,
        robdclark@chromium.org, christian@brauner.io,
        dietmar.eggemann@arm.com, mingo@redhat.com, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, bsegall@google.com, mgorman@suse.de,
        bristot@redhat.com
Cc:     linux-kernel@vger.kernel.org, Yafang Shao <laoar.shao@gmail.com>
Subject: [PATCH v3 3/4] sched.h: extend task comm from 16 to 24 for CONFIG_BASE_FULL
Date:   Sun, 10 Oct 2021 10:24:28 +0000
Message-Id: <20211010102429.99577-4-laoar.shao@gmail.com>
In-Reply-To: <20211010102429.99577-1-laoar.shao@gmail.com>
References: <20211010102429.99577-1-laoar.shao@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

When I was implementing a new per-cpu kthread cfs_migration, I found the
comm of it "cfs_migration/%u" is truncated due to the limitation of
TASK_COMM_LEN. For example, the comm of the percpu thread on CPU10~19 are
all with the same name "cfs_migration/1", which will confuse the user. This
issue is not critical, because we can get the corresponding CPU from the
task's Cpus_allowed. But for kthreads correspoinding to other hardware
devices, it is not easy to get the detailed device info from task comm,
for example,

    jbd2/nvme0n1p2-
    xfs-reclaim/sdf

We can also shorten the name to work around this problem, but I find
there are so many truncated kthreads:

    rcu_tasks_kthre
    rcu_tasks_rude_
    rcu_tasks_trace
    poll_mpt3sas0_s
    ext4-rsv-conver
    xfs-reclaim/sd{a, b, c, ...}
    xfs-blockgc/sd{a, b, c, ...}
    xfs-inodegc/sd{a, b, c, ...}
    audit_send_repl
    ecryptfs-kthrea
    vfio-irqfd-clea
    jbd2/nvme0n1p2-
    ...

We should improve this problem fundamentally.

This patch extends the size of task comm to 24 bytes, which is the
same length with workqueue's, for the CONFIG_BASE_FULL case. And for the
CONFIG_BASE_SMALL case, the size of task comm is still kept as 16 bytes.

Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Petr Mladek <pmladek@suse.com>
---
 include/linux/sched.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 39039ce8ac4c..e0796068dee0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -275,7 +275,11 @@ struct task_group;
 #define get_current_state()	READ_ONCE(current->__state)
 
 /* Task command name length: */
+#if CONFIG_BASE_SMALL
 #define TASK_COMM_LEN			16
+#else
+#define TASK_COMM_LEN			24
+#endif
 
 extern void scheduler_tick(void);
 
-- 
2.18.2