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

[Yafang Shao]

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>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
---
 include/linux/sched.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 39039ce8ac4c..e0796068dee0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -275,7 +275,11 @@ struct task_group;
 #define get_current_state()	READ_ONCE(current->__state)
 
 /* Task command name length: */
+#if CONFIG_BASE_SMALL
 #define TASK_COMM_LEN			16
+#else
+#define TASK_COMM_LEN			24
+#endif
 
 extern void scheduler_tick(void);
 
-- 
2.18.2