Re: [Xen-devel] [V4 PATCH 2/2] mips/panic: Replace smp_send_stop() with kdump friendly version in panic path

[Corey Minyard <cminyard@xxxxxxxxxx>]

I'll try to test this, but I have one comment inline...

On 08/11/2016 10:17 PM, Dave Young wrote:
> On 08/10/16 at 05:09pm, Hidehiro Kawai wrote:
> > Daniel Walker reported problems which happens when
> > crash_kexec_post_notifiers kernel option is enabled
> > (https://lkml.org/lkml/2015/6/24/44).
> >
> > In that case, smp_send_stop() is called before entering kdump routines
> > which assume other CPUs are still online.  As the result, kdump
> > routines fail to save other CPUs' registers.  Additionally for MIPS
> > OCTEON, it misses to stop the watchdog timer.
> >
> > To fix this problem, call a new kdump friendly function,
> > crash_smp_send_stop(), instead of the smp_send_stop() when
> > crash_kexec_post_notifiers is enabled.  crash_smp_send_stop() is a
> > weak function, and it just call smp_send_stop().  Architecture
> > codes should override it so that kdump can work appropriately.
> > This patch provides MIPS version.
> >
> > Reported-by: Daniel Walker <dwalker@xxxxxxxxxx>
> > Fixes: f06e5153f4ae (kernel/panic.c: add "crash_kexec_post_notifiers" option)
> > Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@xxxxxxxxxxx>
> > Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
> > Cc: David Daney <david.daney@xxxxxxxxxx>
> > Cc: Aaro Koskinen <aaro.koskinen@xxxxxx>
> > Cc: "Steven J. Hill" <steven.hill@xxxxxxxxxx>
> > Cc: Corey Minyard <cminyard@xxxxxxxxxx>
> >
> > ---
> > I'm not familiar with MIPS, and I don't have a test environment and
> > just did build tests only.  Please don't apply this patch until
> > someone does enough tests, otherwise simply drop this patch.
> > ---
> >   arch/mips/cavium-octeon/setup.c  |   14 ++++++++++++++
> >   arch/mips/include/asm/kexec.h    |    1 +
> >   arch/mips/kernel/crash.c         |   18 +++++++++++++++++-
> >   arch/mips/kernel/machine_kexec.c |    1 +
> >   4 files changed, 33 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/mips/cavium-octeon/setup.c b/arch/mips/cavium-octeon/setup.c
> > index cb16fcc..5537f95 100644
> > --- a/arch/mips/cavium-octeon/setup.c
> > +++ b/arch/mips/cavium-octeon/setup.c
> > @@ -267,6 +267,17 @@ static void octeon_crash_shutdown(struct pt_regs *regs)
> >         default_machine_crash_shutdown(regs);
> >   }
> >   
> > +#ifdef CONFIG_SMP
> > +void octeon_crash_smp_send_stop(void)
> > +{
> > +       int cpu;
> > +
> > +       /* disable watchdogs */
> > +       for_each_online_cpu(cpu)
> > +               cvmx_write_csr(CVMX_CIU_WDOGX(cpu_logical_map(cpu)), 0);
> > +}
> > +#endif
> > +
> >   #endif /* CONFIG_KEXEC */
> >   
> >   #ifdef CONFIG_CAVIUM_RESERVE32
> > @@ -911,6 +922,9 @@ void __init prom_init(void)
> >         _machine_kexec_shutdown = octeon_shutdown;
> >         _machine_crash_shutdown = octeon_crash_shutdown;
> >         _machine_kexec_prepare = octeon_kexec_prepare;
> > +#ifdef CONFIG_SMP
> > +       _crash_smp_send_stop = octeon_crash_smp_send_stop;
> > +#endif
> >   #endif
> >   
> >   	octeon_user_io_init();
> > diff --git a/arch/mips/include/asm/kexec.h b/arch/mips/include/asm/kexec.h
> > index ee25ebb..493a3cc 100644
> > --- a/arch/mips/include/asm/kexec.h
> > +++ b/arch/mips/include/asm/kexec.h
> > @@ -45,6 +45,7 @@ extern const unsigned char kexec_smp_wait[];
> >   extern unsigned long secondary_kexec_args[4];
> >   extern void (*relocated_kexec_smp_wait) (void *);
> >   extern atomic_t kexec_ready_to_reboot;
> > +extern void (*_crash_smp_send_stop)(void);
> >   #endif
> >   #endif
> >   
> > 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.

-corey

> > +
> > +       ncpus = num_online_cpus() - 1;/* Excluding the panic cpu */
> >   
> >   	dump_send_ipi(crash_shutdown_secondary);
> >         smp_wmb();
> > @@ -64,6 +69,17 @@ static void crash_kexec_prepare_cpus(void)
> >                 cpu_relax();
> >                 mdelay(1);
> >         }
> > +
> > +       cpus_stopped = 1;
> > +}
> > +
> > +/* Override the weak function in kernel/panic.c */
> > +void crash_smp_send_stop(void)
> > +{
> > +       if (_crash_smp_send_stop)
> > +               _crash_smp_send_stop();
> > +
> > +       crash_kexec_prepare_cpus();
> >   }
> >   
> >   #else /* !defined(CONFIG_SMP)  */
> > diff --git a/arch/mips/kernel/machine_kexec.c b/arch/mips/kernel/machine_kexec.c
> > index 50980bf3..5972520 100644
> > --- a/arch/mips/kernel/machine_kexec.c
> > +++ b/arch/mips/kernel/machine_kexec.c
> > @@ -25,6 +25,7 @@ void (*_machine_crash_shutdown)(struct pt_regs *regs) = NULL;
> >   #ifdef CONFIG_SMP
> >   void (*relocated_kexec_smp_wait) (void *);
> >   atomic_t kexec_ready_to_reboot = ATOMIC_INIT(0);
> > +void (*_crash_smp_send_stop)(void) = NULL;
> >   #endif
> >   
> >   int
> Can any mips people review this patch and have a test?
>
> Thanks
> Dave

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