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,