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Subject: Re: [PATCH] powerpc/xive: Do not skip CPU-less nodes when creating
 the IPIs
To: =?UTF-8?Q?C=c3=a9dric_Le_Goater?= <clg@kaod.org>,
 linuxppc-dev@lists.ozlabs.org
References: <20210629131542.743888-1-clg@kaod.org>
From: Laurent Vivier <lvivier@redhat.com>
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Date: Wed, 7 Jul 2021 19:37:25 +0200
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Cc: Geetika Moolchandani <Geetika.Moolchandani1@ibm.com>,
 Srikar Dronamraju <srikar@linux.vnet.ibm.com>, stable@vger.kernel.org
Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org
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 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

On 29/06/2021 15:15, Cédric Le Goater wrote:
> On PowerVM, CPU-less nodes can be populated with hot-plugged CPUs at
> runtime. Today, the IPI is not created for such nodes, and hot-plugged
> CPUs use a bogus IPI, which leads to soft lockups.
>
> We could create the node IPI on demand but it is a bit complex because
> this code would be called under bringup_up() and some IRQ locking is
> being done. The simplest solution is to create the IPIs for all nodes
> at startup.
>
> Fixes: 7dcc37b3eff9 ("powerpc/xive: Map one IPI interrupt per node")
> Cc: stable@vger.kernel.org # v5.13
> Reported-by: Geetika Moolchandani <Geetika.Moolchandani1@ibm.com>
> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> Signed-off-by: Cédric Le Goater <clg@kaod.org>
> ---
>
> This patch breaks old versions of irqbalance (<= v1.4). Possible nodes
> are collected from /sys/devices/system/node/ but CPU-less nodes are
> not listed there. When interrupts are scanned, the link representing
> the node structure is NULL and segfault occurs.
>
> Version 1.7 seems immune. 
>
> ---
>  arch/powerpc/sysdev/xive/common.c | 4 ----
>  1 file changed, 4 deletions(-)
>
> diff --git a/arch/powerpc/sysdev/xive/common.c b/arch/powerpc/sysdev/xive/common.c
> index f3b16ed48b05..5d2c58dba57e 100644
> --- a/arch/powerpc/sysdev/xive/common.c
> +++ b/arch/powerpc/sysdev/xive/common.c
> @@ -1143,10 +1143,6 @@ static int __init xive_request_ipi(void)
>  		struct xive_ipi_desc *xid = &xive_ipis[node];
>  		struct xive_ipi_alloc_info info = { node };
>  
> -		/* Skip nodes without CPUs */
> -		if (cpumask_empty(cpumask_of_node(node)))
> -			continue;
> -
>  		/*
>  		 * Map one IPI interrupt per node for all cpus of that node.
>  		 * Since the HW interrupt number doesn't have any meaning,

Tested-by: Laurent Vivier <lvivier@redhat.com>