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f9619d5e51
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 commit9ea69a55b3("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
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.