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    blk-mq: ensure that bd->last is always set correctly · 113285b4
    Jens Axboe 提交于
    When drivers are called with a request in blk-mq, blk-mq flags the
    state such that the driver knows if this is the last request in
    this call chain or not. The driver can then use that information
    to defer kicking off IO until bd->last is true. However, with blk-mq
    and scheduling, we need to allocate a driver tag for a request before
    it can be issued. If we fail to allocate such a tag, we could end up
    in the situation where the last request issued did not have
    bd->last == true set. This can then cause a driver hang.
    
    This fixes a hang with virtio-blk, which uses bd->last as a hint
    on whether to kick the queue or not.
    Reported-by: NChris Mason <clm@fb.com>
    Tested-by: NChris Mason <clm@fb.com>
    Reviewed-by: NOmar Sandoval <osandov@fb.com>
    Signed-off-by: NJens Axboe <axboe@fb.com>
    113285b4
blk-mq.c 69.9 KB