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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 9ea69a5 ("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: 9ea69a5 ("powerpc/pseries: Pass MSI affinity to irq_create_mapping()") Cc: [email protected] # v5.10+ Signed-off-by: Greg Kurz <[email protected]> Reviewed-by: Laurent Vivier <[email protected]> Reviewed-by: Cédric Le Goater <[email protected]> Signed-off-by: Michael Ellerman <[email protected]> Link: https://lore.kernel.org/r/[email protected]
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