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authorGreg Kurz <groug@kaod.org>2021-02-15 10:45:06 +0100
committerMichael Ellerman <mpe@ellerman.id.au>2021-03-01 12:33:31 +1100
commitf9619d5e5174867536b7e558683bc4408eab833f (patch)
tree61e7af565c6b74141368cfa8413e75009235dd05 /arch
parenteead089311f4d935ab5d1d8fbb0c42ad44699ada (diff)
downloadlinux-f9619d5e5174867536b7e558683bc4408eab833f.tar.bz2
powerpc/pseries: Don't enforce MSI affinity with kdump
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: 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
Diffstat (limited to 'arch')
-rw-r--r--arch/powerpc/platforms/pseries/msi.c25
1 files changed, 23 insertions, 2 deletions
diff --git a/arch/powerpc/platforms/pseries/msi.c b/arch/powerpc/platforms/pseries/msi.c
index b3ac2455faad..637300330507 100644
--- a/arch/powerpc/platforms/pseries/msi.c
+++ b/arch/powerpc/platforms/pseries/msi.c
@@ -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 @@ again:
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);