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@xxxxxxxxx/
>
> 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@xxxxxxxxxx>
--
Thanks,
David / dhildenb
