On 08/15/2016 06:35 AM, ???? / KAWAI?HIDEHIRO wrote: > Hi Corey, > >> From: Corey Minyard [mailto:cminyard at 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! > >> 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 >
