powerpc/rtas: avoid scheduling in rtas_os_term()

JIRA: https://issues.redhat.com/browse/RHEL-81040

commit 6c606e5
Author: Nathan Lynch <nathanl@linux.ibm.com>
Date:   Fri Nov 18 09:07:42 2022 -0600

    powerpc/rtas: avoid scheduling in rtas_os_term()

    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>
    Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
    Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://lore.kernel.org/r/20221118150751.469393-5-nathanl@linux.ibm.com

Signed-off-by: Mamatha Inamdar <minamdar@redhat.com>

Author: Mamatha Inamdar

arch/powerpc/kernel/rtas.c

@@ -862,11 +862,16 @@ 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 {
 		rtas_call_unlocked(&args, rtas_token("ibm,os-term"), 1, 1, NULL,
 				   __pa(rtas_os_term_buf));
 		status = be32_to_cpu(args.rets[0]);
-	} 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);