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

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

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

--
Kees Cook

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