Hi,
commit 1959a60182f4 ("x86/dumpstack: Pin the target stack when dumping
it") slightly changed the behaviour of stack traces dumping for zombie
tasks.
Before the commit (well, this is older SLE12 kernel, but that should not
matter), if one called 'cat /proc/<zombie pid>/stack', they would get
something like this
[<ffffffff8105b877>] do_exit+0x6f7/0xa80
[<ffffffff8105bc79>] do_group_exit+0x39/0xa0
[<ffffffff8105bcf0>] __wake_up_parent+0x0/0x30
[<ffffffff8152dd09>] system_call_fastpath+0x16/0x1b
[<00007fd128f9c4f9>] 0x7fd128f9c4f9
[<ffffffffffffffff>] 0xffffffffffffffff
After, one gets nothing. The trace is empty. try_get_task_stack() contains
atomic_inc_not_zero() (CONFIG_THREAD_INFO_IN_TASK is now default on
x86_64) and because stack_refcount is 0 for a zombie task, it returns
NULL. Therefore, all save_stack_trace_*() functions return immediately.
I guess that no one has cared about it so far. There is a problem for
live patching though. save_stack_trace_tsk_reliable() returns -EINVAL for
the zombie task and its stack is deemed unreliable. It could block our
transition for quite a long time.
We can skip those tasks in kernel/livepatch/ with a simple test we have in
kGraft. Skip the task if (task->state == TASK_DEAD && task->on_cpu == 0).
But you may want to change it generally, so better to ask first.
Regards,
Miroslav
--
To unsubscribe from this list: send the line "unsubscribe live-patching" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
