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

[Yafang Shao]

On Thu, Oct 7, 2021 at 10:56 PM Kees Cook <keescook@xxxxxxxxxxxx> 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@xxxxxxxx>
> > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
>
> 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@xxxxxxxxxxxx>
>

Thanks for the review.

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

-- 
Thanks
Yafang