Re: [PATCH 04/13] powerpc/rtas: avoid scheduling in rtas_os_term()

[Andrew Donnellan <ajd@linux.ibm.com>]

On Fri, 2022-11-18 at 09:07 -0600, Nathan Lynch wrote:
> It's unsafe to use rtas_busy_delay() to handle a busy status from
> the ibm,os-term RTAS function in rtas_os_term():
> 
> Kernel panic - not syncing: Attempted to kill init!
> exitcode=0x0000000b
> BUG: sleeping function called from invalid context at
> arch/powerpc/kernel/rtas.c:618
> in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 1, name:
> swapper/0
> preempt_count: 2, expected: 0
> CPU: 7 PID: 1 Comm: swapper/0 Tainted: G      D            6.0.0-rc5-
> 02182-gf8553a572277-dirty #9
> Call Trace:
> [c000000007b8f000] [c000000001337110] dump_stack_lvl+0xb4/0x110
> (unreliable)
> [c000000007b8f040] [c0000000002440e4] __might_resched+0x394/0x3c0
> [c000000007b8f0e0] [c00000000004f680] rtas_busy_delay+0x120/0x1b0
> [c000000007b8f100] [c000000000052d04] rtas_os_term+0xb8/0xf4
> [c000000007b8f180] [c0000000001150fc] pseries_panic+0x50/0x68
> [c000000007b8f1f0] [c000000000036354]
> ppc_panic_platform_handler+0x34/0x50
> [c000000007b8f210] [c0000000002303c4] notifier_call_chain+0xd4/0x1c0
> [c000000007b8f2b0] [c0000000002306cc]
> atomic_notifier_call_chain+0xac/0x1c0
> [c000000007b8f2f0] [c0000000001d62b8] panic+0x228/0x4d0
> [c000000007b8f390] [c0000000001e573c] do_exit+0x140c/0x1420
> [c000000007b8f480] [c0000000001e586c] make_task_dead+0xdc/0x200
> 
> Use rtas_busy_delay_time() instead, which signals without side
> effects
> whether to attempt the ibm,os-term RTAS call again.
> 
> Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>

Makes sense.

Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>

> ---
>  arch/powerpc/kernel/rtas.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
> index 81e4996012b7..51f0508593a7 100644
> --- a/arch/powerpc/kernel/rtas.c
> +++ b/arch/powerpc/kernel/rtas.c
> @@ -965,10 +965,15 @@ void rtas_os_term(char *str)
>  
>         snprintf(rtas_os_term_buf, 2048, "OS panic: %s", str);
>  
> +       /*
> +        * Keep calling as long as RTAS returns a "try again" status,
> +        * but don't use rtas_busy_delay(), which potentially
> +        * schedules.
> +        */
>         do {
>                 status = rtas_call(ibm_os_term_token, 1, 1, NULL,
>                                    __pa(rtas_os_term_buf));
> -       } while (rtas_busy_delay(status));
> +       } while (rtas_busy_delay_time(status));
>  
>         if (status != 0)
>                 printk(KERN_EMERG "ibm,os-term call failed %d\n",
> status);

-- 
Andrew Donnellan    OzLabs, ADL Canberra
ajd@linux.ibm.com   IBM Australia Limited