[PATCH] Move precessing of MCE queued event out from syscall exit path.

[Hugh Dickins]

On Tue, 14 Jan 2014, Mahesh J Salgaonkar wrote:
> From: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
> 
> Huge Dickins reported an issue that b5ff4211a829
> "powerpc/book3s: Queue up and process delayed MCE events" breaks the
> PowerMac G5 boot. This patch fixes it by moving the mce even processing
> away from syscall exit, which was wrong to do that in first place, and
> implements a different mechanism to deal with it using a paca flag and
> decrementer interrupt to process the event.
> 
> Reported-by: Hugh Dickins <hughd at google.com>
> Signed-off-by: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>

Good work guys: I can happily report that both this rework,
and Ben's one-liner, fix the issue for me on the G5: thank you.

(Irrelevant not-so-happy detail: I very nearly mailed you an hour or
so earlier to report that neither fixed it; but retried my original
CONFIG_PPC_POWERNV hack after, and found that now equally useless.

I did write of changing behaviour and ATA errors: it now appears that's
an independent but intermittent issue on the G5 in 3.13-rc7-mm1, which
coincidentally happened to trigger when I tested rc7-mm1 without fixes,
but not when I tested with my hack, until today.

I've gone back to testing on rc6-mm1, the previous week's mmotm,
which showed failure to run /sbin/init: rc6-mm1 has no trouble mounting
root, and it runs properly with your new patch, and with Ben's patch.

And I may be quite wrong to point a finger at ATA errors: perhaps
they're always shown, and quickly cleared off screen in successful boots,
but left visible when root cannot be mounted for some other reason.

I don't know, and won't have time to investigate further - bisecting
intermittents is not much fun!  I'll just have to hope that it's
sorted out before it reaches 3.14-rc, or else bite the bullet and
investigate on that.)

Hugh

> ---
>  arch/powerpc/include/asm/mce.h  |    3 +++
>  arch/powerpc/include/asm/paca.h |    3 +++
>  arch/powerpc/kernel/entry_64.S  |    5 -----
>  arch/powerpc/kernel/irq.c       |   11 ++++++++++-
>  arch/powerpc/kernel/mce.c       |    7 +++++++
>  arch/powerpc/kernel/time.c      |    9 +++++++++
>  6 files changed, 32 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/mce.h b/arch/powerpc/include/asm/mce.h
> index 2257d1e..225e678 100644
> --- a/arch/powerpc/include/asm/mce.h
> +++ b/arch/powerpc/include/asm/mce.h
> @@ -186,6 +186,9 @@ struct mce_error_info {
>  #define MCE_EVENT_RELEASE	true
>  #define MCE_EVENT_DONTRELEASE	false
>  
> +/* MCE bit flags (paca.mce_flags) */
> +#define MCE_EVENT_PENDING	0x0001
> +
>  extern void save_mce_event(struct pt_regs *regs, long handled,
>  			   struct mce_error_info *mce_err, uint64_t nip,
>  			   uint64_t addr);
> diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
> index c3523d1..f9aa521 100644
> --- a/arch/powerpc/include/asm/paca.h
> +++ b/arch/powerpc/include/asm/paca.h
> @@ -141,6 +141,9 @@ struct paca_struct {
>  	u8 io_sync;			/* writel() needs spin_unlock sync */
>  	u8 irq_work_pending;		/* IRQ_WORK interrupt while soft-disable */
>  	u8 nap_state_lost;		/* NV GPR values lost in power7_idle */
> +#ifdef CONFIG_PPC_BOOK3S_64
> +	u8 mce_flags;			/* MCE bit flags. */
> +#endif
>  	u64 sprg3;			/* Saved user-visible sprg */
>  #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
>  	u64 tm_scratch;                 /* TM scratch area for reclaim */
> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> index 770d6d6..bbfb029 100644
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -184,11 +184,6 @@ syscall_exit:
>  	bl	.do_show_syscall_exit
>  	ld	r3,RESULT(r1)
>  #endif
> -#ifdef CONFIG_PPC_BOOK3S_64
> -BEGIN_FTR_SECTION
> -	bl	.machine_check_process_queued_event
> -END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
> -#endif
>  	CURRENT_THREAD_INFO(r12, r1)
>  
>  	ld	r8,_MSR(r1)
> diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
> index ba01656..e22f591 100644
> --- a/arch/powerpc/kernel/irq.c
> +++ b/arch/powerpc/kernel/irq.c
> @@ -67,6 +67,7 @@
>  #include <asm/udbg.h>
>  #include <asm/smp.h>
>  #include <asm/debug.h>
> +#include <asm/mce.h>
>  
>  #ifdef CONFIG_PPC64
>  #include <asm/paca.h>
> @@ -158,9 +159,17 @@ notrace unsigned int __check_irq_replay(void)
>  	 * We may have missed a decrementer interrupt. We check the
>  	 * decrementer itself rather than the paca irq_happened field
>  	 * in case we also had a rollover while hard disabled
> +	 * Also check if any MCE event is queued up that requires
> +	 * processing. Machine check handler would set paca->mce_flags
> +	 * and then call set_dec(1) to trigger a decrementer interrupt
> +	 * from NMI.
>  	 */
>  	local_paca->irq_happened &= ~PACA_IRQ_DEC;
> -	if ((happened & PACA_IRQ_DEC) || decrementer_check_overflow())
> +	if ((happened & PACA_IRQ_DEC) || decrementer_check_overflow()
> +#ifdef CONFIG_PPC_BOOK3S_64
> +		|| local_paca->mce_flags & MCE_EVENT_PENDING
> +#endif
> +		)
>  		return 0x900;
>  
>  	/* Finally check if an external interrupt happened */
> diff --git a/arch/powerpc/kernel/mce.c b/arch/powerpc/kernel/mce.c
> index d6edf2b..7bab827 100644
> --- a/arch/powerpc/kernel/mce.c
> +++ b/arch/powerpc/kernel/mce.c
> @@ -185,6 +185,13 @@ void machine_check_queue_event(void)
>  		return;
>  	}
>  	__get_cpu_var(mce_event_queue[index]) = evt;
> +
> +	/*
> +	 * Set the event pending flag and raise an decrementer interrupt
> +	 * to process the queued event later.
> +	 */
> +	local_paca->mce_flags |= MCE_EVENT_PENDING;
> +	set_dec(1);
>  }
>  
>  /*
> diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
> index b3b1441..87ccf92 100644
> --- a/arch/powerpc/kernel/time.c
> +++ b/arch/powerpc/kernel/time.c
> @@ -69,6 +69,7 @@
>  #include <asm/vdso_datapage.h>
>  #include <asm/firmware.h>
>  #include <asm/cputime.h>
> +#include <asm/mce.h>
>  
>  /* powerpc clocksource/clockevent code */
>  
> @@ -505,6 +506,14 @@ void timer_interrupt(struct pt_regs * regs)
>  		return;
>  	}
>  
> +#ifdef CONFIG_PPC_BOOK3S_64
> +	/* Check if we have MCE event pending for processing. */
> +	if (local_paca->mce_flags & MCE_EVENT_PENDING) {
> +		local_paca->mce_flags &= ~MCE_EVENT_PENDING;
> +		machine_check_process_queued_event();
> +	}
> +#endif
> +
>  	/* Conditionally hard-enable interrupts now that the DEC has been
>  	 * bumped to its maximum value
>  	 */