linux-kernel - [PATCH v2] ARM:kexec:offline panic_smp_self

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Date:   Fri, 2 Nov 2018 10:31:27 +0800
From:   wangyufen <wangyufen@...wei.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <akpm@...ux-foundation.org>,
        <kstewart@...uxfoundation.org>, <rppt@...ux.vnet.ibm.com>,
        <gregkh@...uxfoundation.org>, <tglx@...utronix.de>,
        <pombredanne@...b.com>, <weiyongjun1@...wei.com>,
        <huawei.libin@...wei.com>, Wangyufen <wangyufen@...wei.com>
Subject: [PATCH v2] ARM:kexec:offline panic_smp_self_stop CPU

In case panic() and panic() called at the same time on different CPUS.
For example:
CPU 0:
  panic()
     __crash_kexec
       machine_crash_shutdown
         crash_smp_send_stop
       machine_kexec
         BUG_ON(num_online_cpus() > 1);

CPU 1:
  panic()
    local_irq_disable
    panic_smp_self_stop

If CPU 1 calls panic_smp_self_stop() before crash_smp_send_stop(), kdump
fails. CPU1 can't receive the ipi irq, CPU1 will be always online.
To fix this problem, this patch split out the panic_smp_self_stop()
and add set_cpu_online(smp_processor_id(), false).

Signed-off-by: Yufen Wang <wangyufen@...wei.com>
---
 arch/arm/kernel/smp.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 9000d8b..d7b86e4 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -682,6 +682,21 @@ void smp_send_stop(void)
 		pr_warn("SMP: failed to stop secondary CPUs\n");
 }
 
+/* In case panic() and panic() called at the same time on CPU1 and CPU2,
+ * and CPU 1 calls panic_smp_self_stop() before crash_smp_send_stop()
+ * CPU1 can't receive the ipi irqs from CPU2, CPU1 will be always online,
+ * kdump fails. So split out the panic_smp_self_stop() and add
+ * set_cpu_online(smp_processor_id(), false).
+ */
+void panic_smp_self_stop(void)
+{
+	pr_debug("CPU %u will stop doing anything useful since another CPU has paniced\n",
+	         smp_processor_id());
+	set_cpu_online(smp_processor_id(), false);
+	while (1)
+		cpu_relax();
+}
+
 /*
  * not supported here
  */
-- 
2.7.4