Prev: [rfc] new stat*fs-like syscall?
Next: mfd/stmpexxx: change touchscreen irq
From: Peter Zijlstra on 24 Jun 2010 09:20
On Thu, 2010-06-24 at 00:11 +0400, Ilya Loginov wrote:
> There is a bug in rest_init function. The problem is that kernel_init
> thread starts before initialization of kthreadd_task when
> CONFIG_PREEMPT_VOLUNTARY is enabled.
>
> kernel_init thread do wake_up_process(kthreadd_task) and I have kernel Oops in
> try_to_wake_up when I try to get p->state.
>
> I found this problem on 2.6.34 on FPGA. It is very slow, and
> find_task_by_pid is done after reschenduling. I have no this problem on
> 2.6.35-rc3 because kernel code is moved. But if I write simple loop like
> volatile int tmp;
> for(i = 0; i < preset_lpj; i++)
> tmp++;
> right after kernel_thread(kernel_init,.... , I have this problem on
> 2.6.35-rc3 too.
>
> I understand that real problem is reschenduling in init code, but
> I have no ability to fix it.

Ooh, interesting problem, so kernel_init() will indeed spawn all kinds
of kernel threads, and doing so before we create the kthreadd will
result in the oops you observed.

However I suspect the ordering is like it is because we want init to
have pid 1, if we were to re-order like you suggest kthreadd will end up
with pid 1 and init with pid 2.

Humm, how to fix this...

> Signed-off-by: Ilya Loginov <isloginov(a)gmail.com>
> ---
> diff --git a/init/main.c b/init/main.c
> index 3bdb152..9febd69 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -428,12 +428,12 @@ static noinline void __init_refok rest_init(void)
> int pid;
>
> rcu_scheduler_starting();
> - kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
> numa_default_policy();
> pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
> rcu_read_lock();
> kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
> rcu_read_unlock();
> + kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
> unlock_kernel();
>
> /*

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
From: Ilya Loginov on 24 Jun 2010 09:30
On Thu, 24 Jun 2010 15:11:36 +0200
Peter Zijlstra <peterz(a)infradead.org> wrote:

> However I suspect the ordering is like it is because we want init to
> have pid 1, if we were to re-order like you suggest kthreadd will end up
> with pid 1 and init with pid 2.

Strange, but init does not die after I did this. Fix me if I wrong, but it wants
to have pid 1, and die in other case.

Interesting...

--
Ilya Loginov <isloginov(a)gmail.com>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
From: Илья Логинов on 24 Jun 2010 10:10
On Thu, 24 Jun 2010 17:23:34 +0400
Ilya Loginov <isloginov(a)gmail.com> wrote:

> Strange, but init does not die after I did this. Fix me if I wrong, but it wants
> to have pid 1, and die in other case.
>
> Interesting...

Yeah, of course, I am wrong. To make it clear I watched sources of sysvinit and
founded out that if pid not equal to 1 init does

exit(telinit(p, argc, argv));

So, it does not die. Anyway, I would have kernel panic.

--
éÌØÑ ìÏÇÉÎÏ× <zerone2(a)gmail.com>
 | 
Pages: 1
Prev: [rfc] new stat*fs-like syscall?
Next: mfd/stmpexxx: change touchscreen irq