Re: [PATCHv3 4/7] block: Introduce a dedicated lock for protecting queue elevator updates

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On 2/24/25 14:30, 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@xxxxxxxxxx/

Signed-off-by: Nilay Shroff <nilay@xxxxxxxxxxxxx>
---
  block/blk-core.c       |  1 +
  block/blk-mq.c         | 15 +++++++--------
  block/blk-sysfs.c      | 32 ++++++++++++++++++++++----------
  block/elevator.c       | 35 ++++++++++++++++-------------------
  block/elevator.h       |  2 --
  block/genhd.c          |  9 ++++++---
  include/linux/blkdev.h |  5 +++++
  7 files changed, 57 insertions(+), 42 deletions(-)

Reviewed-by: Hannes Reinecke <hare@xxxxxxx>

Cheers,

Hannes
--
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@xxxxxxx                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich




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