blk-mq: fix possible deadlocks #535
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To move implementation details inside blk-wbt.c, prepare to fix possible deadlock to call wbt_init() while queue is frozen in the next patch. Reviewed-by: Ming Lei <[email protected]> Reviewed-by: Nilay Shroff <[email protected]> Signed-off-by: Yu Kuai <[email protected]> Reviewed-by: Hannes Reinecke <[email protected]>
…_counter If wbt is disabled by default and user configures wbt by sysfs, queue will be frozen first and then pcpu_alloc_mutex will be held in blk_stat_alloc_callback(). Fix this problem by allocating memory first before queue frozen. Signed-off-by: Yu Kuai <[email protected]> Reviewed-by: Nilay Shroff <[email protected]> Reviewed-by: Ming Lei <[email protected]>
There is already a helper blk_mq_debugfs_register_rqos() to register one rqos, however this helper is called synchronously when the rqos is created with queue frozen. Prepare to fix possible deadlock to create blk-mq debugfs entries while queue is still frozen. Reviewed-by: Ming Lei <[email protected]> Reviewed-by: Nilay Shroff <[email protected]> Signed-off-by: Yu Kuai <[email protected]> Reviewed-by: Hannes Reinecke <[email protected]>
Currently rq-qos debugfs entries are created from rq_qos_add(), while rq_qos_add() can be called while queue is still frozen. This can deadlock because creating new entries can trigger fs reclaim. Fix this problem by delaying creating rq-qos debugfs entries after queue is unfrozen. - For wbt, 1) it can be initialized by default, fix it by calling new helper after wbt_init() from wbt_init_enable_default(); 2) it can be initialized by sysfs, fix it by calling new helper after queue is unfrozen from wbt_set_lat(). - For iocost and iolatency, they can only be initialized by blkcg configuration, however, they don't have debugfs entries for now, hence they are not handled yet. Signed-off-by: Yu Kuai <[email protected]> Reviewed-by: Nilay Shroff <[email protected]> Reviewed-by: Ming Lei <[email protected]> Reviewed-by: Hannes Reinecke <[email protected]>
Because it's only used inside blk-mq-debugfs.c now. Reviewed-by: Nilay Shroff <[email protected]> Signed-off-by: Yu Kuai <[email protected]> Reviewed-by: Ming Lei <[email protected]> Reviewed-by: Hannes Reinecke <[email protected]>
Because this helper is only used by iocost and iolatency, while they don't have debugfs entries. Signed-off-by: Yu Kuai <[email protected]> Reviewed-by: Nilay Shroff <[email protected]> Reviewed-by: Ming Lei <[email protected]> Reviewed-by: Hannes Reinecke <[email protected]>
…hctxs() In blk_mq_update_nr_hw_queues(), debugfs_mutex is not held while creating debugfs entries for hctxs. Hence add debugfs_mutex there, it's safe because queue is not frozen. Signed-off-by: Yu Kuai <[email protected]> Reviewed-by: Nilay Shroff <[email protected]> Reviewed-by: Ming Lei <[email protected]> Reviewed-by: Hannes Reinecke <[email protected]>
Creating new debugfs entries can trigger fs reclaim, hence we can't do this with queue frozen, meanwhile, other locks that can be held while queue is frozen should not be held as well. Signed-off-by: Yu Kuai <[email protected]> Reviewed-by: Nilay Shroff <[email protected]> Reviewed-by: Ming Lei <[email protected]> Reviewed-by: Hannes Reinecke <[email protected]>
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Pull request for series with
subject: blk-mq: fix possible deadlocks
version: 9
url: https://patchwork.kernel.org/project/linux-block/list/?series=1049630