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

[Will Deacon]

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:
> > 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@mail.gmail.com

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

Will