On 08/15/2016 12:06 PM, Corey Minyard wrote:

On 08/15/2016 06:35 AM, 河合英宏 / KAWAI，HIDEHIRO wrote:

quoted

Hi Corey,

quoted

From: Corey Minyard [mailto:cminyard@mvista.com]
Sent: Friday, August 12, 2016 10:56 PM
I'll try to test this, but I have one comment inline...

Thank you very much!

quoted

On 08/11/2016 10:17 PM, Dave Young wrote:

quoted

On 08/10/16 at 05:09pm, Hidehiro Kawai wrote:

[snip]

quoted

quoted

quoted

diff --git a/arch/mips/kernel/crash.c b/arch/mips/kernel/crash.c
index 610f0f3..1723b17 100644
--- a/arch/mips/kernel/crash.c
+++ b/arch/mips/kernel/crash.c

@@ -47,9 +47,14 @@ static void crash_shutdown_secondary(void 

*passed_regs)

   static void crash_kexec_prepare_cpus(void)
   {
+    static int cpus_stopped;
       unsigned int msecs;
+    unsigned int ncpus;

-    unsigned int ncpus = num_online_cpus() - 1;/* Excluding the 
panic cpu */
+    if (cpus_stopped)
+        return;

Wouldn't you want an atomic operation and some special handling here to
ensure that only one CPU does this?  So if a CPU comes in here and
another CPU is already in the process stopping the CPUs it won't 
result in a
deadlock.

Because this function can be called only one panicking CPU,
there is no problem.

There are two paths which crash_kexec_prepare_cpus is called.

Path 1 (panic path):
panic()
   crash_smp_send_stop()
     crash_kexec_prepare_cpus()

Path 2 (oops path):
crash_kexec()
   __crash_kexec()
     machine_crash_shutdown()
       default_machine_crash_shutdown() // for MIPS
         crash_kexec_prepare_cpus()

Here, panic() and crash_kexec() run exclusively via
panic_cpu atomic variable.  So we can use cpus_stopped as
normal variable.

Ok, if the code can only be entered once, what's the purpose of 
cpus_stopped?
I guess that's what confused me.  You are right, the panic_cpu atomic 
should
keep this on a single CPU.

Never mind, I see the path through panic() where that is required. My 
question
below still remains, though.

-corey

Also, panic() will call panic_smp_self_stop() if it finds another CPU 
has already
called panic, which will just spin with interrupts off by default. I 
didn't see a
definition for it in MIPS, wouldn't it need to be overridden to avoid 
a deadlock?

-corey

quoted

Best regards,

Hidehiro Kawai