Re: [PATCH v2] kexec: Fix kdump failure with notsc

[Xunlei Pang <xpang@redhat.com>]

On 2016/07/07 at 18:17, Wei Jiangang wrote:
> If we specify the 'notsc' boot parameter for the dump-capture kernel,
> and then trigger a crash(panic) by using "ALT-SysRq-c" or "echo c >
> /proc/sysrq-trigger",
> the dump-capture kernel will hang in calibrate_delay_converge():
>
>     /* wait for "start of" clock tick */
>     ticks = jiffies;
>     while (ticks == jiffies)
>         ; /* nothing */
>
> serial log of the hang is as follows:
>
>     tsc: Fast TSC calibration using PIT
>     tsc: Detected 2099.947 MHz processor
>     Calibrating delay loop...
>
> The reason is that the dump-capture kernel hangs in while loops and
> waits for jiffies to be updated, but no timer interrupts is passed
> to BSP by APIC.
>
> In fact, the local APIC was disabled in reboot and crash path by
> lapic_shutdown(). We need to put APIC in legacy mode in kexec jump path
> (put the system into PIT during the crash kernel),
> so that the dump-capture kernel can get timer interrupts.
>
> BTW,
> I found the buggy commit 522e66464467 ("x86/apic: Disable I/O APIC
> before shutdown of the local APIC") via bisection.
>
> Originally, I want to revert it.
> But Ingo Molnar comments that "By reverting the change can paper over
> the bug, but re-introduce the bug that can result in certain CPUs hanging
> if IO-APIC sends an APIC message if the lapic is disabled prematurely"
> And I think it's pertinent.
>
> Signed-off-by: Wei Jiangang <weijg.fnst@cn.fujitsu.com>
> ---
>  arch/x86/include/asm/apic.h        | 5 +++++
>  arch/x86/kernel/apic/apic.c        | 9 +++++++++
>  arch/x86/kernel/machine_kexec_32.c | 5 ++---
>  arch/x86/kernel/machine_kexec_64.c | 6 +++---
>  4 files changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
> index bc27611fa58f..5d7e635e580a 100644
> --- a/arch/x86/include/asm/apic.h
> +++ b/arch/x86/include/asm/apic.h
> @@ -128,6 +128,7 @@ extern void clear_local_APIC(void);
>  extern void disconnect_bsp_APIC(int virt_wire_setup);
>  extern void disable_local_APIC(void);
>  extern void lapic_shutdown(void);
> +extern int lapic_disabled(void);
>  extern void sync_Arb_IDs(void);
>  extern void init_bsp_APIC(void);
>  extern void setup_local_APIC(void);
> @@ -165,6 +166,10 @@ extern int setup_APIC_eilvt(u8 lvt_off, u8 vector, u8 msg_type, u8 mask);
>  
>  #else /* !CONFIG_X86_LOCAL_APIC */
>  static inline void lapic_shutdown(void) { }
> +static inline int lapic_disabled(void)
> +{
> +	return 0;
> +}
>  #define local_apic_timer_c2_ok		1
>  static inline void init_apic_mappings(void) { }
>  static inline void disable_local_APIC(void) { }
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 60078a67d7e3..d1df250994bb 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -133,6 +133,9 @@ static inline void imcr_apic_to_pic(void)
>  }
>  #endif
>  
> +/* Local APIC is disabled by the kernel for crash or reboot path */
> +static int disabled_local_apic;
> +
>  /*
>   * Knob to control our willingness to enable the local APIC.
>   *
> @@ -1097,10 +1100,16 @@ void lapic_shutdown(void)
>  #endif
>  		disable_local_APIC();
>  
> +	disabled_local_apic = 1;
>  
>  	local_irq_restore(flags);
>  }
>  
> +int lapic_disabled(void)
> +{
> +	return disabled_local_apic;
> +}
> +
>  /**
>   * sync_Arb_IDs - synchronize APIC bus arbitration IDs
>   */
> diff --git a/arch/x86/kernel/machine_kexec_32.c b/arch/x86/kernel/machine_kexec_32.c
> index 469b23d6acc2..c934a7868e6b 100644
> --- a/arch/x86/kernel/machine_kexec_32.c
> +++ b/arch/x86/kernel/machine_kexec_32.c
> @@ -202,14 +202,13 @@ void machine_kexec(struct kimage *image)
>  	local_irq_disable();
>  	hw_breakpoint_disable();
>  
> -	if (image->preserve_context) {
> +	if (image->preserve_context || lapic_disabled()) {
>  #ifdef CONFIG_X86_IO_APIC
>  		/*
>  		 * We need to put APICs in legacy mode so that we can
>  		 * get timer interrupts in second kernel. kexec/kdump
>  		 * paths already have calls to disable_IO_APIC() in
> -		 * one form or other. kexec jump path also need
> -		 * one.
> +		 * one form or other. kexec jump path also need one.
>  		 */
>  		disable_IO_APIC();

Hi Wei,

As the comment says, kexec/kdump paths already have disable_IO_APIC(), why again here?

Regards,
Xunlei

>  #endif
> diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
> index 5a294e48b185..d3598cdd6437 100644
> --- a/arch/x86/kernel/machine_kexec_64.c
> +++ b/arch/x86/kernel/machine_kexec_64.c
> @@ -23,6 +23,7 @@
>  #include <asm/pgtable.h>
>  #include <asm/tlbflush.h>
>  #include <asm/mmu_context.h>
> +#include <asm/apic.h>
>  #include <asm/io_apic.h>
>  #include <asm/debugreg.h>
>  #include <asm/kexec-bzimage64.h>
> @@ -269,14 +270,13 @@ void machine_kexec(struct kimage *image)
>  	local_irq_disable();
>  	hw_breakpoint_disable();
>  
> -	if (image->preserve_context) {
> +	if (image->preserve_context || lapic_disabled()) {
>  #ifdef CONFIG_X86_IO_APIC
>  		/*
>  		 * We need to put APICs in legacy mode so that we can
>  		 * get timer interrupts in second kernel. kexec/kdump
>  		 * paths already have calls to disable_IO_APIC() in
> -		 * one form or other. kexec jump path also need
> -		 * one.
> +		 * one form or other. kexec jump path also need one.
>  		 */
>  		disable_IO_APIC();
>  #endif