[PATCH v9 1/6] arm64: Add macros to manage processor debug state

On Wed, Feb 19, 2014 at 04:03:59PM +0000, Catalin Marinas wrote:

On Wed, Feb 19, 2014 at 11:31:57AM +0000, Catalin Marinas wrote:

quoted

BUG: scheduling while atomic: kworker/u8:0/6/0x00000002
Modules linked in:
CPU: 1 PID: 6 Comm: kworker/u8:0 Not tainted 3.14.0-rc3+ #306
Workqueue: khelper __call_usermodehelper
Call trace:
[<ffffffc000087dbc>] dump_backtrace+0x0/0x12c
[<ffffffc000087efc>] show_stack+0x14/0x1c
[<ffffffc00043c224>] dump_stack+0x78/0xc4
[<ffffffc000439b48>] __schedule_bug+0x40/0x54
[<ffffffc00043d67c>] __schedule+0x514/0x604
[<ffffffc00043d794>] schedule+0x28/0x78
[<ffffffc00043cc90>] schedule_timeout+0x170/0x1bc
[<ffffffc00043e16c>] wait_for_common+0xc0/0x14c
[<ffffffc00043e280>] wait_for_completion_killable+0x14/0x28
[<ffffffc0000942f8>] do_fork+0x158/0x2a8
[<ffffffc000094478>] kernel_thread+0x30/0x38
[<ffffffc0000a842c>] __call_usermodehelper+0x34/0xa8
[<ffffffc0000ab300>] process_one_work+0x118/0x354
[<ffffffc0000abfcc>] worker_thread+0x13c/0x3c0
[<ffffffc0000b1e84>] kthread+0xd4/0xe8


It gets much worse if I run with two CPUs and CONFIG_KGDB_KDB enabled
(but fine with a single CPU).

So no need to post another series for now but please check the multi-CPU
case as well and send a separate fix. I'll dig a bit on my side as well.

So far I'm done with the investigation. It looks to me like one of the
kgdb tests, kgdb core or the arm64 back-end (or maybe more than one) is
not SMP safe. The errors either appear or disappear based on the printks
I put through the kgdb test or other config options which I enable.

Could you please look into making the kgdb back-end SMP-safe?

There are certainly potential SMP problems in the back-end, which I asked
about in the initial series:

  http://lkml.kernel.org/r/CALicx6v1eGHRwWPrjzihzBZxCu8t1vpMoq-YfutSm4mRmP6gEQ at mail.gmail.com

The reply from Vijay suggested that everything is confined to a single CPU.

Will