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blk-mq: create correct map for fallback case

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The fallback code in blk_mq_map_hw_queues is original from
blk_mq_pci_map_queues and was added to handle the case where
pci_irq_get_affinity will return NULL for !SMP configuration.

blk_mq_map_hw_queues replaces besides blk_mq_pci_map_queues also
blk_mq_virtio_map_queues which used to use blk_mq_map_queues for the
fallback.

It's possible to use blk_mq_map_queues for both cases though.
blk_mq_map_queues creates the same map as blk_mq_clear_mq_map for !SMP
that is CPU 0 will be mapped to hctx 0.

The WARN_ON_ONCE has to be dropped for virtio as the fallback is also
taken for certain configuration on default. Though there is still a
WARN_ON_ONCE check in lib/group_cpus.c:

       WARN_ON(nr_present + nr_others < numgrps);

which will trigger if the caller tries to create more hardware queues
than CPUs. It tests the same as the WARN_ON_ONCE in
blk_mq_pci_map_queues did.

Fixes: a5665c3d150c ("virtio: blk/scsi: replace blk_mq_virtio_map_queues with blk_mq_map_hw_queues")
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Closes: https://lore.kernel.org/all/20250122093020.6e8a4e5b@gandalf.local.home/
Signed-off-by: Daniel Wagner <wagi@kernel.org>
Link: https://lore.kernel.org/r/20250123-fix-blk_mq_map_hw_queues-v1-1-08dbd01f2c39@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Daniel Wagner 2025-01-23 14:08:29 +01:00 committed by Jens Axboe
parent b13ee668e8
commit a9ae6fe1c3
1 changed files with 1 additions and 2 deletions
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3
block/blk-mq-cpumap.c
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@ -87,7 +87,6 @@ void blk_mq_map_hw_queues(struct blk_mq_queue_map *qmap,
return;
fallback:
WARN_ON_ONCE(qmap->nr_queues > 1);
blk_mq_clear_mq_map(qmap);
blk_mq_map_queues(qmap);
}
EXPORT_SYMBOL_GPL(blk_mq_map_hw_queues);