block: lift the initial queue bypass mode on blk_register_queue() instead of...
block: lift the initial queue bypass mode on blk_register_queue() instead of blk_init_allocated_queue() b82d4b19 ("blkcg: make request_queue bypassing on allocation") made request_queues bypassed on allocation to avoid switching on and off bypass mode on a queue being initialized. Some drivers allocate and then destroy a lot of queues without fully initializing them and incurring bypass latency overhead on each of them could add upto significant overhead. Unfortunately, blk_init_allocated_queue() is never used by queues of bio-based drivers, which means that all bio-based driver queues are in bypass mode even after initialization and registration complete successfully. Due to the limited way request_queues are used by bio drivers, this problem is hidden pretty well but it shows up when blk-throttle is used in combination with a bio-based driver. Trying to configure (echoing to cgroupfs file) blk-throttle for a bio-based driver hangs indefinitely in blkg_conf_prep() waiting for bypass mode to end. This patch moves the initial blk_queue_bypass_end() call from blk_init_allocated_queue() to blk_register_queue() which is called for any userland-visible queues regardless of its type. I believe this is correct because I don't think there is any block driver which needs or wants working elevator and blk-cgroup on a queue which isn't visible to userland. If there are such users, we need a different solution. Signed-off-by: NTejun Heo <tj@kernel.org> Reported-by: NJoseph Glanville <joseph.glanville@orionvm.com.au> Cc: stable@vger.kernel.org Acked-by: NVivek Goyal <vgoyal@redhat.com> Signed-off-by: NJens Axboe <axboe@kernel.dk>
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