Hi, 河合英宏

Thanks for the patch log update, it looks good to me.

Acked-by: Dave Young <redacted>

On 09/20/16 at 11:22am, 河合英宏 / KAWAI，HIDEHIRO wrote:

Here is the revised commit description reflecting Dave's
comment.  Cc list was copied from -mm version.

From: Hidehiro Kawai <redacted>
Subject: x86/panic: replace smp_send_stop() with kdump friendly version in panic path

This patch fixes a problem reported by Daniel Walker
(https://lkml.org/lkml/2015/6/24/44).

When kernel panics with crash_kexec_post_notifiers kernel parameter
enabled, other CPUs are stopped by smp_send_stop() instead of
machine_crash_shutdown() in __crash_kexec() path.

  panic()
    if crash_kexec_post_notifiers == 1
      smp_send_stop()
      atomic_notifier_call_chain()
      kmsg_dump()
    __crash_kexec()
      machine_crash_shutdown()

Different from smp_send_stop(), machine_crash_shutdown() stops other
CPUs with extra works for kdump.  So, if smp_send_stop() stops other
CPUs in advance, these extra works won't be done.  For x86, kdump
routines miss to save other CPUs' registers and disable virtualization
extensions.

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 only provides x86-specific version.

For Xen's PV kernel, just keep the current behavior.
As for Dom0, it doesn't use crash_kexec routines, and it relies on
panic notifier chain.  At the end of the chain, a hypercall is
issued which requests the hypervisor to execute kdump.  This means
regardless of crash_kexec_post_notifiers setting, smp_send_stop().
For PV HVM, it would work similarly to baremetal kernels with extra
cleanups for hypervisor.  It doesn't need additional care.

Changes in V4:
- Keep to use smp_send_stop if crash_kexec_post_notifiers is not set
- Rename panic_smp_send_stop to crash_smp_send_stop
- Don't change the behavior for Xen's PV kernel

Changes in V3:
- Revise comments, description, and symbol names

Changes in V2:
- Replace smp_send_stop() call with crash_kexec version which
  saves cpu states and cleans up VMX/SVM
- Drop a fix for Problem 1 at this moment

Fixes: f06e5153f4ae (kernel/panic.c: add "crash_kexec_post_notifiers" option)
Link: http://lkml.kernel.org/r/20160810080948.11028.15344.stgit@sysi4-13.yrl.intra.hitachi.co.jp
Signed-off-by: Hidehiro Kawai <redacted>
Reported-by: Daniel Walker <redacted>
Cc: Dave Young <redacted>
Cc: Baoquan He <redacted>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Eric Biederman <redacted>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Daniel Walker <redacted>
Cc: Xunlei Pang <redacted>
Cc: Thomas Gleixner <redacted>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Borislav Petkov <redacted>
Cc: David Vrabel <redacted>
Cc: Toshi Kani <redacted>
Cc: Ralf Baechle <redacted>
Cc: David Daney <redacted>
Cc: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: "Steven J. Hill" <redacted>
Cc: Corey Minyard <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

[snip]

Thanks
Dave