On 2016/07/12 at 15:12, ???? / KAWAI?HIDEHIRO wrote: >> From: linux-kernel-owner at vger.kernel.org [mailto:linux-kernel-owner at vger.kernel.org] On Behalf Of Xunlei Pang >> Sent: Tuesday, July 12, 2016 3:57 PM >> On 2016/07/12 at 11:56, ???? / KAWAI?HIDEHIRO wrote: >>> Hi Xunlei, >>> >>> Thanks for the review. >>> >>>> From: Xunlei Pang [mailto:xpang at redhat.com] >>>> Sent: Tuesday, July 12, 2016 12:12 PM >>>> On 2016/07/05 at 19:33, Hidehiro Kawai wrote: >>>>> This patch fixes one of the problems reported by Daniel Walker >>>>> (https://lkml.org/lkml/2015/6/24/44). >>>>> >>>>> If crash_kexec_post_notifiers boot option is specified, other CPUs >>>>> are stopped by smp_send_stop() instead of machine_crash_shutdown() >>>>> in crash_kexec() path. This behavior change leads two problems. >>>>> >>>>> Problem 1: >>>>> octeon_generic_shutdown() for MIPS OCTEON assumes that other CPUs are >>>>> still online and try to stop their watchdog timer. If >>>>> smp_send_stop() is called before octeon_generic_shutdown(), stopping >>>>> watchdog timer will fail because other CPUs have been offlined by >>>>> smp_send_stop(). >>>>> >>>>> panic() >>>>> if crash_kexec_post_notifiers == 1 >>>>> smp_send_stop() >>>>> atomic_notifier_call_chain() >>>>> kmsg_dump() >>>>> crash_kexec() >>>>> machine_crash_shutdown() >>>>> octeon_generic_shutdown() // shutdown watchdog for ONLINE CPUs >>>>> >>>>> Problem 2: >>>>> Most of architectures stop other CPUs in machine_crash_shutdown() >>>>> path, and they also do something needed for kdump. For example, >>>>> they save registers, disable virtualization extensions, and so on. >>>>> However, if smp_send_stop() stops other CPUs before >>>>> machine_crash_shutdown(), we miss those operations. >>>>> >>>>> How do we fix these problems? In the first place, we should stop >>>>> other CPUs as soon as possible when panic() was called, otherwise >>>>> other CPUs may wipe out a clue to the cause of the failure. So, we >>>>> replace smp_send_stop() with more suitable one for kdump. >>>>> >>>>> This patch solves Problem 2 by replacing smp_send_stop() in panic() >>>>> with panic_smp_send_stop(). This is a weak function which calls >>>>> smp_send_stop(), and architecture dependent code may override this >>>>> with appropriate one. This patch only provides x86-specific version. >>>>> >>>>> 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 >>>>> >>>>> Reported-by: Daniel Walker <dwalker at fifo99.com> >>>>> Fixes: f06e5153f4ae (kernel/panic.c: add "crash_kexec_post_notifiers" option) >>>>> Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez at hitachi.com> >>>>> Cc: Dave Young <dyoung at redhat.com> >>>>> Cc: Baoquan He <bhe at redhat.com> >>>>> Cc: Vivek Goyal <vgoyal at redhat.com> >>>>> Cc: Eric Biederman <ebiederm at xmission.com> >>>>> Cc: Masami Hiramatsu <mhiramat at kernel.org> >>>>> Cc: Thomas Gleixner <tglx at linutronix.de> >>>>> Cc: Ingo Molnar <mingo at redhat.com> >>>>> Cc: "H. Peter Anvin" <hpa at zytor.com> >>>>> Cc: Borislav Petkov <bp at suse.de> >>>>> Cc: Toshi Kani <toshi.kani at hpe.com> >>>>> Cc: "Peter Zijlstra (Intel)" <peterz at infradead.org> >>>>> Cc: Takao Indoh <indou.takao at jp.fujitsu.com> >>>>> Cc: "Lee, Chun-Yi" <joeyli.kernel at gmail.com> >>>>> Cc: Minfei Huang <mnfhuang at gmail.com> >>>>> Cc: Andrew Morton <akpm at linux-foundation.org> >>>>> Cc: Michal Hocko <mhocko at suse.com> >>>>> Cc: Vitaly Kuznetsov <vkuznets at redhat.com> >>>>> Cc: Petr Mladek <pmladek at suse.com> >>>>> Cc: Tejun Heo <tj at kernel.org> >>>>> Cc: Josh Poimboeuf <jpoimboe at redhat.com> >>>>> --- >>>>> arch/x86/kernel/crash.c | 14 ++++++++++---- >>>>> kernel/panic.c | 43 ++++++++++++++++++++++++++++++++----------- >>>>> 2 files changed, 42 insertions(+), 15 deletions(-) >>>>> >>>>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c >>>>> index 9ef978d..3305433 100644 >>>>> --- a/arch/x86/kernel/crash.c >>>>> +++ b/arch/x86/kernel/crash.c >>>>> @@ -133,15 +133,21 @@ static void kdump_nmi_callback(int cpu, struct pt_regs *regs) >>>>> disable_local_APIC(); >>>>> } >>>>> >>>>> -static void kdump_nmi_shootdown_cpus(void) >>>>> +/* Override the weak function in kernel/panic.c */ >>>>> +void panic_smp_send_stop(void) >>>>> { >>>>> - nmi_shootdown_cpus(kdump_nmi_callback); >>>>> + static int cpus_stopped; >>>> Should be atomic_t type? >>> panic_smp_send_stop() can be called by only one panicking CPU >>> (but can be called twice). It is sufficient to be normal variable. >> There are other call sites of __crash_kexec() for oops cases, which can >> call panic_smp_send_stop() concurrently on a different cpu. > In oops cases, crash_kexec() is called first, then __crash_kexec() is > called. crash_kexec() excludes concurrent execution of panic() and > crash_kexec() via panic_cpu, so panic_smp_send_stop() shouldn't be > called concurrently. Right, that's why oops calls crash_kexec() not __crash_kexec(). I have no problem on this. Thanks! Regards, Xunlei
