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From: David Hildenbrand <david@redhat.com>
To: Yafang Shao <laoar.shao@gmail.com>, akpm@linux-foundation.org
Cc: netdev@vger.kernel.org, bpf@vger.kernel.org,
	linux-perf-users@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	oliver.sang@intel.com, lkp@intel.com,
	Petr Mladek <pmladek@suse.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Andrii Nakryiko <andrii.nakryiko@gmail.com>,
	Michal Miroslaw <mirq-linux@rere.qmqm.pl>,
	Peter Zijlstra <peterz@infradead.org>,
	Matthew Wilcox <willy@infradead.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH v2] kthread: dynamically allocate memory to store kthread's full name
Date: Thu, 25 Nov 2021 10:36:49 +0100	[thread overview]
Message-ID: <435fab0b-d345-3698-79af-ff858181666a@redhat.com> (raw)
In-Reply-To: <20211120112850.46047-1-laoar.shao@gmail.com>

On 20.11.21 12:28, 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-
>     xfs-reclaim/sdf
> 
> Currently 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 can shorten these names to work around this problem, but it may be
> not applied to all of the truncated kthreads. Take 'jbd2/nvme0n1p2-' for
> example, it is a nice name, and it is not a good idea to shorten it.
> 
> One possible way to fix this issue is extending the task comm size, but
> as task->comm is used in lots of places, that may cause some potential
> buffer overflows. Another more conservative approach is introducing a new
> pointer to store kthread's full name if it is truncated, which won't
> introduce too much overhead as it is in the non-critical path. Finally we
> make a dicision to use the second approach. See also the discussions in
> this thread:
> https://lore.kernel.org/lkml/20211101060419.4682-1-laoar.shao@gmail.com/
> 
> After this change, the full name of these truncated kthreads will be
> displayed via /proc/[pid]/comm:
> 
>     rcu_tasks_kthread
>     rcu_tasks_rude_kthread
>     rcu_tasks_trace_kthread
>     poll_mpt3sas0_statu
>     ext4-rsv-conversion
>     xfs-reclaim/sdf1
>     xfs-blockgc/sdf1
>     xfs-inodegc/sdf1
>     audit_send_reply
>     ecryptfs-kthread
>     vfio-irqfd-cleanup
>     jbd2/nvme0n1p2-8

I do wonder if that could break some user space that assumes these names
have maximum length ..

But LGTM

Reviewed-by: David Hildenbrand <david@redhat.com>


-- 
Thanks,

David / dhildenb


  parent reply	other threads:[~2021-11-25  9:38 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-20 11:28 Yafang Shao
2021-11-25  9:18 ` Petr Mladek
2021-11-25  9:36 ` David Hildenbrand [this message]
2021-11-25 14:46   ` Petr Mladek
2021-11-25 14:47     ` David Hildenbrand

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