linux-kernel - [PATCH AUTOSEL 6.0 22/27] powerpc/rtas: avoid scheduling in rtas_os

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Date:   Tue, 27 Dec 2022 15:33:37 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Nathan Lynch <nathanl@...ux.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Andrew Donnellan <ajd@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Sasha Levin <sashal@...nel.org>, ldufour@...ux.ibm.com,
        sourabhjain@...ux.ibm.com, paulus@...abs.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH AUTOSEL 6.0 22/27] powerpc/rtas: avoid scheduling in rtas_os_term()

From: Nathan Lynch <nathanl@...ux.ibm.com>

[ Upstream commit 6c606e57eecc37d6b36d732b1ff7e55b7dc32dd4 ]

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@...ux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@...il.com>
Reviewed-by: Andrew Donnellan <ajd@...ux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Link: https://lore.kernel.org/r/20221118150751.469393-5-nathanl@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 082b0c9e0c8a..5a873d4fbd7b 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -892,10 +892,15 @@ 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);
-- 
2.35.1