Re: [PATCH v2 3/4] sched.h: extend task comm from 16 to 24 for CONFIG_BASE_FULL

From: Yafang Shao <laoar.shao@gmail.com>
To: Kees Cook <keescook@chromium.org>
Cc: Petr Mladek <pmladek@suse.com>, Al Viro <viro@zeniv.linux.org.uk>,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	qiang.zhang@windriver.com, robdclark@chromium.org,
	christian@brauner.io, Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Benjamin Segall <bsegall@google.com>,
	Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 3/4] sched.h: extend task comm from 16 to 24 for CONFIG_BASE_FULL
Date: Thu, 7 Oct 2021 23:47:09 +0800	[thread overview]
Message-ID: <CALOAHbAFZRUPn-kpgtm1Qi-ro2y=fJn3am94ho5N+f6HTxj9wA@mail.gmail.com> (raw)
In-Reply-To: <202110070755.60DFB87711@keescook>

On Thu, Oct 7, 2021 at 10:56 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Thu, Oct 07, 2021 at 12:07:51PM +0000, Yafang Shao wrote:
> > 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-
> >     nvidia-modeset/
> >
> > 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-
> >     ...
> >
> > Besides the in-tree kthreads listed above, the out-of-tree kthreads may
> > also be truncated:
> >
> >     rtase_work_queu
> >     nvidia-modeset/
> >     UVM global queu
> >     UVM deferred re
> >     ...
> >
> > 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>
>
> This, as expected, adds 8 bytes to task_struct, which is reasonable. I
> don't see any easy places to consolidate other members to make this a
> "free" change, but I did just remove 64 bytes from task_struct[1], so
> this is okay. :)
>

Cool!

> Reviewed-by: Kees Cook <keescook@chromium.org>
>

Thanks for the review.

> [1] https://lore.kernel.org/lkml/20210924025450.4138503-1-keescook@chromium.org/
>

-- 
Thanks
Yafang