block/blk-rq-qos: fix incorrect lock order for rq_qos_mutex and freeze queue #375
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queue should not be freezed under rq_qos_mutex, see example index commit 9730763 ("block: correct locking order for protecting blk-wbt parameters"), which means current implementation of rq_qos_add() is problematic. Add a new helper and prepare to fix this problem in following patches. Signed-off-by: Yu Kuai <yukuai@fnnas.com> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
wbt_init() can be called from sysfs attribute and wbt_enable_default(), however the lock order are inversely. - queue_wb_lat_store() freeze queue first, and then wbt_init() hold rq_qos_mutex. In this case queue will be freezed again inside rq_qos_add(), however, in this case freeze queue recursivly is inoperative; - wbt_enable_default() from elevator switch will hold rq_qos_mutex first, and then rq_qos_add() will freeze queue; Fix this problem by converting to use new helper rq_qos_add_freezed() in wbt_init(), and for wbt_enable_default(), freeze queue before calling wbt_init(). Fixes: a13bd91 ("block/rq_qos: protect rq_qos apis with a new lock") Signed-off-by: Yu Kuai <yukuai@fnnas.com> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Like wbt, rq_qos_add() can be called from two path and the lock order are inversely: - From ioc_qos_write(), queue is already freezed before rq_qos_add(); - From ioc_cost_model_write(), rq_qos_add() is called directly; Fix this problem by converting to use blkg_conf_open_bdev_frozen() from ioc_cost_model_write(), then since all rq_qos_add() callers already freeze queue, convert to use rq_qos_add_freezed. Signed-off-by: Yu Kuai <yukuai@fnnas.com> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
…ueue Currently blk-iolatency will hold rq_qos_mutex first and then call rq_qos_add() to freeze queue. Fix this problem by converting to use blkg_conf_open_bdev_frozen() from iolatency_set_limit(), and convert to use rq_qos_add_freezed(). Signed-off-by: Yu Kuai <yukuai@fnnas.com> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Now that there is no caller of rq_qos_add(), remove it, and also rename rq_qos_add_freezed() back to rq_qos_add(). Signed-off-by: Yu Kuai <yukuai@fnnas.com> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
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Pull request for series with
subject: block/blk-rq-qos: fix incorrect lock order for rq_qos_mutex and freeze queue
version: 1
url: https://patchwork.kernel.org/project/linux-block/list/?series=1023924