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authorOmar Sandoval <osandov@fb.com>2017-04-07 08:56:26 -0600
committerJens Axboe <axboe@fb.com>2017-04-07 08:56:26 -0600
commit81380ca10778b99dce98940cfc993214712df335 (patch)
treece167a1c5f914d91949af26cfb4f38d964d3daa5 /block/elevator.c
parent8945927cb7cc5953cc1554053452f50248159c88 (diff)
downloadlinux-0-day-81380ca10778b99dce98940cfc993214712df335.tar.gz
blk-mq: use the right hctx when getting a driver tag fails
While dispatching requests, if we fail to get a driver tag, we mark the hardware queue as waiting for a tag and put the requests on a hctx->dispatch list to be run later when a driver tag is freed. However, blk_mq_dispatch_rq_list() may dispatch requests from multiple hardware queues if using a single-queue scheduler with a multiqueue device. If blk_mq_get_driver_tag() fails, it doesn't update the hardware queue we are processing. This means we end up using the hardware queue of the previous request, which may or may not be the same as that of the current request. If it isn't, the wrong hardware queue will end up waiting for a tag, and the requests will be on the wrong dispatch list, leading to a hang. The fix is twofold: 1. Make sure we save which hardware queue we were trying to get a request for in blk_mq_get_driver_tag() regardless of whether it succeeds or not. 2. Make blk_mq_dispatch_rq_list() take a request_queue instead of a blk_mq_hw_queue to make it clear that it must handle multiple hardware queues, since I've already messed this up on a couple of occasions. This didn't appear in testing with nvme and mq-deadline because nvme has more driver tags than the default number of scheduler tags. However, with the blk_mq_update_nr_hw_queues() fix, it showed up with nbd. Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
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