• Ming Lei's avatar
    blk-mq: insert passthrough request into hctx->dispatch directly · 01e99aec
    Ming Lei authored
    For some reason, device may be in one situation which can't handle
    FS request, so STS_RESOURCE is always returned and the FS request
    will be added to hctx->dispatch. However passthrough request may
    be required at that time for fixing the problem. If passthrough
    request is added to scheduler queue, there isn't any chance for
    blk-mq to dispatch it given we prioritize requests in hctx->dispatch.
    Then the FS IO request may never be completed, and IO hang is caused.
    
    So passthrough request has to be added to hctx->dispatch directly
    for fixing the IO hang.
    
    Fix this issue by inserting passthrough request into hctx->dispatch
    directly together withing adding FS request to the tail of
    hctx->dispatch in blk_mq_dispatch_rq_list(). Actually we add FS request
    to tail of hctx->dispatch at default, see blk_mq_request_bypass_insert().
    
    Then it becomes consistent with original legacy IO request
    path, in which passthrough request is always added to q->queue_head.
    
    Cc: Dongli Zhang <dongli.zhang@oracle.com>
    Cc: Christoph Hellwig <hch@infradead.org>
    Cc: Ewan D. Milne <emilne@redhat.com>
    Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    01e99aec
blk-mq.h 7.64 KB