Subject: [PATCH AUTOSEL 5.10 23/34] powerpc: handle kdump appropriately with crash_kexec_post_notifiers option

From: Sasha Levin <[email-masked]>
Date: Mon, 17 Jan 2022 12:03:13 -0500

From: Hari Bathini <[email-masked]>

[ Upstream commit 219572d2fc4135b5ce65c735d881787d48b10e71 ]

Kdump can be triggered after panic_notifers since commit f06e5153f4ae2
("kernel/panic.c: add "crash_kexec_post_notifiers" option for kdump
after panic_notifers") introduced crash_kexec_post_notifiers option.
But using this option would mean smp_send_stop(), that marks all other
CPUs as offline, gets called before kdump is triggered. As a result,
kdump routines fail to save other CPUs' registers. To fix this, kdump
friendly crash_smp_send_stop() function was introduced with kernel
commit 0ee59413c967 ("x86/panic: replace smp_send_stop() with kdump
friendly version in panic path"). Override this kdump friendly weak
function to handle crash_kexec_post_notifiers option appropriately
on powerpc.

Reported-by: kernel test robot <[email-masked]>
Signed-off-by: Hari Bathini <[email-masked]>
[Fixed signature of crash_stop_this_cpu() - reported by [email-masked]]
Signed-off-by: Michael Ellerman <[email-masked]>
Link: https://lore.kernel.org/r/[email-masked]
Signed-off-by: Sasha Levin <[email-masked]>
---
 arch/powerpc/kernel/smp.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 50aeef08aa470..d993f28107afa 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -594,6 +594,36 @@ void crash_send_ipi(void (*crash_ipi_callback)(struct pt_regs *))
 }
 #endif
 
+#ifdef CONFIG_NMI_IPI
+static void crash_stop_this_cpu(struct pt_regs *regs)
+#else
+static void crash_stop_this_cpu(void *dummy)
+#endif
+{
+	/*
+	 * Just busy wait here and avoid marking CPU as offline to ensure
+	 * register data is captured appropriately.
+	 */
+	while (1)
+		cpu_relax();
+}
+
+void crash_smp_send_stop(void)
+{
+	static bool stopped = false;
+
+	if (stopped)
+		return;
+
+	stopped = true;
+
+#ifdef CONFIG_NMI_IPI
+	smp_send_nmi_ipi(NMI_IPI_ALL_OTHERS, crash_stop_this_cpu, 1000000);
+#else
+	smp_call_function(crash_stop_this_cpu, NULL, 0);
+#endif /* CONFIG_NMI_IPI */
+}
+
 #ifdef CONFIG_NMI_IPI
 static void nmi_stop_this_cpu(struct pt_regs *regs)
 {
-- 
2.34.1