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powerpc/pseries: Don't enforce MSI affinity with kdump

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commit f9619d5e5174867536b7e558683bc4408eab833f upstream.

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 9ea69a55b3 ("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: 9ea69a55b3 ("powerpc/pseries: Pass MSI affinity to irq_create_mapping()")
Cc: stable@vger.kernel.org # v5.10+
Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210215094506.1196119-1-groug@kaod.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Greg Kurz 2021-02-15 10:45:06 +01:00 committed by Greg Kroah-Hartman
parent ac022fbee6
commit a9c55f22a0
1 changed files with 23 additions and 2 deletions
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25
arch/powerpc/platforms/pseries/msi.c
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@ -4,6 +4,7 @@
* Copyright 2006-2007 Michael Ellerman, IBM Corp.
*/
#include <linux/crash_dump.h>
#include <linux/device.h>
#include <linux/irq.h>
#include <linux/msi.h>
@ -458,8 +459,28 @@ 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);