@@ -458,8 +458,28 @@ static int rtas_setup_msi_irqs(struct pci_dev *pdev, int nvec_in, int type)
return hwirq;
}
- virq = irq_create_mapping_affinity(NULL, hwirq,
- entry->affinity);
+ /*
+ * Depending on the number of online CPUs in the original
+ * kernel, it is likely for CPU #0 to be offline in a kdump
+ * kernel. The associated IRQs in the affinity mappings
+ * provided by irq_create_affinity_masks() are thus not
+ * started by irq_startup(), as per-design for managed IRQs.
+ * This can be a problem with multi-queue block devices driven
+ * by blk-mq : such a non-started IRQ is very likely paired
+ * with the single queue enforced by blk-mq during kdump (see
+ * blk_mq_alloc_tag_set()). This causes the device to remain
+ * silent and likely hangs the guest at some point.
+ *
+ * We don't really care for fine-grained affinity when doing
+ * kdump actually : simply ignore the pre-computed affinity
+ * masks in this case and let the default mask with all CPUs
+ * be used when creating the IRQ mappings.
+ */
+ if (is_kdump_kernel())
+ virq = irq_create_mapping(NULL, hwirq);
+ else
+ virq = irq_create_mapping_affinity(NULL, hwirq,
+ entry->affinity);
if (!virq) {
pr_debug("rtas_msi: Failed mapping hwirq %d\n", hwirq);
Depending on the number of online CPUs in the original kernel, it is likely for CPU #0 to be offline in a kdump kernel. The associated IRQs in the affinity mappings provided by irq_create_affinity_masks() are thus not started by irq_startup(), as per-design with managed IRQs. This can be a problem with multi-queue block devices driven by blk-mq : such a non-started IRQ is very likely paired with the single queue enforced by blk-mq during kdump (see blk_mq_alloc_tag_set()). This causes the device to remain silent and likely hangs the guest at some point. This is a regression caused by commit 9ea69a55b3b9 ("powerpc/pseries: Pass MSI affinity to irq_create_mapping()"). Note that this only happens with the XIVE interrupt controller because XICS has a workaround to bypass affinity, which is activated during kdump with the "noirqdistrib" kernel parameter. The issue comes from a combination of factors: - discrepancy between the number of queues detected by the multi-queue block driver, that was used to create the MSI vectors, and the single queue mode enforced later on by blk-mq because of kdump (i.e. keeping all queues fixes the issue) - CPU#0 offline (i.e. kdump always succeed with CPU#0) Given that I couldn't reproduce on x86, which seems to always have CPU#0 online even during kdump, I'm not sure where this should be fixed. Hence going for another approach : fine-grained affinity is for performance and we don't really care about that during kdump. Simply revert to the previous working behavior of ignoring affinity masks in this case only. Fixes: 9ea69a55b3b9 ("powerpc/pseries: Pass MSI affinity to irq_create_mapping()") Cc: lvivier@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Greg Kurz <groug@kaod.org> --- arch/powerpc/platforms/pseries/msi.c | 24 ++++++++++++++++++++++-- 1 file changed, 22 insertions(+), 2 deletions(-)