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. Regards, Xunlei >>> + >>> + if (cpus_stopped) >>> + return; >>> >>> + nmi_shootdown_cpus(kdump_nmi_callback); >>> disable_local_APIC(); >>> + cpus_stopped = 1; >>> } >>> >>> #else >>> -static void kdump_nmi_shootdown_cpus(void) >>> +void panic_smp_send_stop(void) >>> { >>> /* There are no cpus to shootdown */ >>> } >>> @@ -160,7 +166,7 @@ void native_machine_crash_shutdown(struct pt_regs *regs) >>> /* The kernel is broken so disable interrupts */ >>> local_irq_disable(); >>> >>> - kdump_nmi_shootdown_cpus(); >>> + panic_smp_send_stop(); >>> >>> /* >>> * VMCLEAR VMCSs loaded on this cpu if needed. >>> diff --git a/kernel/panic.c b/kernel/panic.c >>> index 8aa7449..da8062d2 100644 >>> --- a/kernel/panic.c >>> +++ b/kernel/panic.c >>> @@ -71,6 +71,32 @@ void __weak nmi_panic_self_stop(struct pt_regs *regs) >>> panic_smp_self_stop(); >>> } >>> >>> +/* >>> + * Stop other CPUs in panic. Architecture dependent code may override this >>> + * with more suitable version. For example, if the architecture supports >>> + * crash dump, it should save registers of each stopped CPU and disable >>> + * per-CPU features such as virtualization extensions. >>> + */ >>> +void __weak panic_smp_send_stop(void) >>> +{ >>> + static int cpus_stopped; >>> + >>> + /* >>> + * This function can be called twice in panic path, but obviously >>> + * we execute this only once. >>> + */ >>> + if (cpus_stopped) >>> + return; >>> + >>> + /* >>> + * Note smp_send_stop is the usual smp shutdown function, which >>> + * unfortunately means it may not be hardened to work in a panic >>> + * situation. >>> + */ >>> + smp_send_stop(); >>> + cpus_stopped = 1; >>> +} >>> + >>> atomic_t panic_cpu = ATOMIC_INIT(PANIC_CPU_INVALID); >>> >>> /* >>> @@ -125,7 +151,7 @@ void panic(const char *fmt, ...) >>> * Only one CPU is allowed to execute the panic code from here. For >>> * multiple parallel invocations of panic, all other CPUs either >>> * stop themself or will wait until they are stopped by the 1st CPU >>> - * with smp_send_stop(). >>> + * with panic_smp_send_stop(). >>> * >>> * `old_cpu == PANIC_CPU_INVALID' means this is the 1st CPU which >>> * comes here, so go ahead. >>> @@ -165,12 +191,7 @@ void panic(const char *fmt, ...) >>> __crash_kexec(NULL); >>> } >>> >>> - /* >>> - * Note smp_send_stop is the usual smp shutdown function, which >>> - * unfortunately means it may not be hardened to work in a panic >>> - * situation. >>> - */ >>> - smp_send_stop(); >>> + panic_smp_send_stop(); >> If crash_kexec_post_notifiers and kdump both are not used, you actually changed the original behaviour, >> it would be better to make it conditionally like: >> if (crash_kexec_post_notifiers) >> panic_smp_send_stop(); // renaming it to crash_smp_send_stop() is better? >> else >> smp_send_stop(); > Dave also pointed about this, and I'll fix it. > > Best regards, > > Hidehiro Kawai > Hitachi, Ltd. Research & Development Group > >>> /* >>> * Run any panic handlers, including those that might need to >>> @@ -198,10 +219,10 @@ void panic(const char *fmt, ...) >>> >>> /* >>> * We may have ended up stopping the CPU holding the lock (in >>> - * smp_send_stop()) while still having some valuable data in the console >>> - * buffer. Try to acquire the lock then release it regardless of the >>> - * result. The release will also print the buffers out. Locks debug >>> - * should be disabled to avoid reporting bad unlock balance when >>> + * panic_smp_send_stop()) while still having some valuable data in the >>> + * console buffer. Try to acquire the lock then release it regardless >>> + * of the result. The release will also print the buffers out. Locks >>> + * debug should be disabled to avoid reporting bad unlock balance when >>> * panic() is not being callled from OOPS. >>> */ >>> debug_locks_off(); >>> >>> >>> >>> _______________________________________________ >>> kexec mailing list >>> kexec at lists.infradead.org >>> http://lists.infradead.org/mailman/listinfo/kexec
