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
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-
...
We should improve this problem fundamentally by extending comm size to
24 bytes. task_struct is growing rather regularly by 8 bytes.
After this change, the truncated kthreads listed above will be
displayed as:
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
As we have converted all the unsafe copy of task comm to the safe one,
this change won't make any trouble to the kernel or the in-tree tools.
The safe one and unsafe one of comm copy as follows,
Unsafe Safe
strlcpy strscpy_pad
strncpy strscpy_pad
bpf_probe_read_kernel bpf_probe_read_kernel_str
bpf_core_read_str
bpf_get_current_comm
perf_event__prepare_comm
prctl(2)
Regarding the possible risk it may take to the out-of-tree user tools, if
the user tools get the task comm through kernel API like prctl(2),
bpf_get_current_comm() and etc, the tools still work well after this
change. While If the user tools get the task comm through direct string
copy, it must make sure the copied string should be with a nul terminator.
Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@xxxxxxxxx>
Cc: Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx>
Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
---
include/linux/sched.h | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 09ac13e54549..a8822e26653e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -276,10 +276,11 @@ struct task_group;
/*
* Define the task command name length as enum, then it can be visible to
- * BPF programs.
+ * BPF programs. The TASK_COMM_LEN_16 is kept for backward-compitability.
*/
enum {
- TASK_COMM_LEN = 16,
+ TASK_COMM_LEN_16 = 16,
+ TASK_COMM_LEN = 24,
};
extern void scheduler_tick(void);
--
2.17.1
