Re: [PATCHv5 4/7] block: introduce a dedicated lock for protecting queue elevator updates

[Ming Lei <ming.lei@redhat.com>]

On Wed, Feb 26, 2025 at 06:09:57PM +0530, Nilay Shroff wrote:
> 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 <hch@lst.de>
> Reviewed-by: Hannes Reinecke <hare@suse.de>
> Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>

Reviewed-by: Ming Lei <ming.lei@redhat.com>


Thanks,
Ming