From 1bf70d08cc3b55abd1763e6dff5855cb8dd8318b Mon Sep 17 00:00:00 2001 From: Nilay Shroff Date: Tue, 4 Mar 2025 15:52:33 +0530 Subject: block: introduce a dedicated lock for protecting queue elevator updates A queue's elevator can be updated either when modifying nr_hw_queues or through the sysfs scheduler attribute. Currently, elevator switching/ updating is protected using q->sysfs_lock, but this has led to lockdep splats[1] due to inconsistent lock ordering between q->sysfs_lock and the freeze-lock in multiple block layer call sites. As the scope of q->sysfs_lock is not well-defined, its (mis)use has resulted in numerous lockdep warnings. To address this, introduce a new q->elevator_lock, dedicated specifically for protecting elevator switches/updates. And we'd now use this new q->elevator_lock instead of q->sysfs_lock for protecting elevator switches/updates. While at it, make elv_iosched_load_module() a static function, as it is only called from elv_iosched_store(). Also, remove redundant parameters from elv_iosched_load_module() function signature. [1] https://lore.kernel.org/all/67637e70.050a0220.3157ee.000c.GAE@google.com/ Reviewed-by: Christoph Hellwig Reviewed-by: Hannes Reinecke Reviewed-by: Ming Lei Signed-off-by: Nilay Shroff Link: https://lore.kernel.org/r/20250304102551.2533767-5-nilay@linux.ibm.com Signed-off-by: Jens Axboe --- include/linux/blkdev.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'include') diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 248416ecd01c..31b1b635c710 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -560,6 +560,14 @@ struct request_queue { struct blk_flush_queue *fq; struct list_head flush_list; + /* + * Protects against I/O scheduler switching, specifically when + * updating q->elevator. To ensure proper locking order during + * an elevator update, first freeze the queue, then acquire + * ->elevator_lock. + */ + struct mutex elevator_lock; + struct mutex sysfs_lock; struct mutex limits_lock; -- cgit v1.2.3