[linux-next] BUG triggered in ptraceme

[Cyrill Gorcunov <gorcunov@gmail.com>]

Hi Oleg! While been testing criu with linux-next we've triggered a BUG.
https://api.travis-ci.org/v3/job/430308998/log.txt

[    2.461618] BUG: sleeping function called from invalid context at security/apparmor/include/cred.h:154
[    2.461794] in_atomic(): 1, irqs_disabled(): 1, pid: 152, name: init
[    2.461890] 1 lock held by init/152:
[    2.461981]  #0: 00000000f30c3fda (tasklist_lock){.+.+}, at: ptrace_traceme+0x1c/0x70
[    2.462114] irq event stamp: 2524
[    2.462242] hardirqs last  enabled at (2523): [<ffffffff98002922>] do_syscall_64+0x12/0x190
[    2.462363] hardirqs last disabled at (2524): [<ffffffff98b8b02f>] _raw_write_lock_irq+0xf/0x40
[    2.462476] softirqs last  enabled at (1904): [<ffffffff98ac79ef>] unix_sock_destructor+0x4f/0xc0
[    2.462586] softirqs last disabled at (1902): [<ffffffff98ac79ef>] unix_sock_destructor+0x4f/0xc0
[    2.462697] CPU: 1 PID: 152 Comm: init Not tainted 4.19.0-rc4-next-20180918+ #1

Which is due to commit

commit 4b105cbbaf7c06e01c27391957dc3c446328d087
Author: Oleg Nesterov <oleg@redhat.com>
Date:   Wed Jun 17 16:27:33 2009 -0700

    ptrace: do not use task_lock() for attach

because now after write_lock_irq(&tasklist_lock); apparmor calls for
traceme and

static inline struct aa_label *begin_current_label_crit_section(void)
{
	struct aa_label *label = aa_current_raw_label();

-->	might_sleep();

Take a look please, once time permit.

	Cyrill