On 08/15/2016 06:35 AM, 河合英宏 / KAWAI，HIDEHIRO wrote:
Hi Corey,
From: Corey Minyard [mailto:cminyard@xxxxxxxxxx]
Sent: Friday, August 12, 2016 10:56 PM
I'll try to test this, but I have one comment inline...
Thank you very much!
On 08/11/2016 10:17 PM, Dave Young wrote:
On 08/10/16 at 05:09pm, Hidehiro Kawai wrote:
[snip]
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.
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
Best regards,
Hidehiro Kawai
