Re: [PATCH] powerpc/xive: Do not skip CPU-less nodes when creating the IPIs
From: Cédric Le Goater <clg@kaod.org>
Date: 2021-08-06 12:29:09
Also in:
stable
On 6/29/21 3:15 PM, 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 <redacted>
Cc: Srikar Dronamraju <redacted>
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.This is an irqbalance regression due to : https://github.com/Irqbalance/irqbalance/pull/172 I will report through an issue. Anyhow, there is a better approach which is to allocate IPIs for all nodes at boot time and do the mapping on demand. Removing the mapping on last use seems more complex though. I will send a v2 after some tests. Thanks, C.
quoted hunk ↗ jump to hunk
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,