linux-kernel - Re: [PATCH v8 1/7] powerpc/mce: Schedule work from irq

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Date:   Sat, 10 Aug 2019 00:25:48 +0530
From:   Mahesh Jagannath Salgaonkar <mahesh@...ux.vnet.ibm.com>
To:     Santosh Sivaraj <santosh@...six.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>
Cc:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Mahesh Salgaonkar <mahesh@...ux.ibm.com>,
        Reza Arbab <arbab@...ux.ibm.com>,
        Balbir Singh <bsingharora@...il.com>,
        Chandan Rajendra <chandan@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        christophe leroy <christophe.leroy@....fr>
Subject: Re: [PATCH v8 1/7] powerpc/mce: Schedule work from irq_work

On 8/7/19 8:26 PM, Santosh Sivaraj wrote:
> schedule_work() cannot be called from MCE exception context as MCE can
> interrupt even in interrupt disabled context.
> 
> fixes: 733e4a4c ("powerpc/mce: hookup memory_failure for UE errors")
> Signed-off-by: Santosh Sivaraj <santosh@...six.org>
> ---
>  arch/powerpc/kernel/mce.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/mce.c b/arch/powerpc/kernel/mce.c
> index b18df633eae9..0ab6fa7cbbbb 100644
> --- a/arch/powerpc/kernel/mce.c
> +++ b/arch/powerpc/kernel/mce.c
> @@ -144,7 +144,6 @@ void save_mce_event(struct pt_regs *regs, long handled,
>  		if (phys_addr != ULONG_MAX) {
>  			mce->u.ue_error.physical_address_provided = true;
>  			mce->u.ue_error.physical_address = phys_addr;
> -			machine_check_ue_event(mce);
>  		}
>  	}
>  	return;
> @@ -275,8 +274,7 @@ static void machine_process_ue_event(struct work_struct *work)
>  	}
>  }
>  /*
> - * process pending MCE event from the mce event queue. This function will be
> - * called during syscall exit.
> + * process pending MCE event from the mce event queue.
>   */
>  static void machine_check_process_queued_event(struct irq_work *work)
>  {
> @@ -292,6 +290,10 @@ static void machine_check_process_queued_event(struct irq_work *work)
>  	while (__this_cpu_read(mce_queue_count) > 0) {
>  		index = __this_cpu_read(mce_queue_count) - 1;
>  		evt = this_cpu_ptr(&mce_event_queue[index]);
> +
> +		if (evt->error_type == MCE_ERROR_TYPE_UE)
> +			machine_check_ue_event(evt);

This will work only for the event that are queued by mce handler, others
will get ignored. I think you should introduce a separate irq work queue
for schedule_work().

Thanks,
-Mahesh.