From: Jens Axboe <axboe@kernel.dk>
Date: Thu, 13 Nov 2025 16:28:00 +0000 (-0700)
Subject: Merge branch 'elevator-switch-6.19' into for-6.19/block
X-Git-Tag: v6.19-rc1~168^2~48
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8e1bf774ab18157cb8041628f2661aa12e425914;p=thirdparty%2Flinux.git

Merge branch 'elevator-switch-6.19' into for-6.19/block

Merge elevator switching improvements from Nilay:

"This patchset reorganizes the elevator switch path used during both
 nr_hw_queues update and elv_iosched_store() operations to address a
 recently reported lockdep splat [1].

 The warning highlights a locking dependency between ->freeze_lock and
 ->elevator_lock on pcpu_alloc_mutex, triggered when the Kyber scheduler
 dynamically allocates its private scheduling data. The fix is to ensure
 that such allocations occur outside the locked sections, thus
 eliminating the dependency chain.

 While working on this, it also became evident that the nr_hw_queue
 update code maintains two disjoint xarrays—one for elevator tags and
 another for elevator type—both serving the same purpose. Unifying these
 into a single elv_change_ctx structure improves clarity and
 maintainability.

 This series therefore implements five patches:
 The first perparatory patch unifies elevator tags and type xarrays. It
 combines both xarrays into a single struct elv_change_ctx, simplifying
 per-queue elevator state management.

 The second patch is aimed to group together all elevator-related
 resources that share the same lifetime and as a first step we move the
 elevator tags pointer from struct elv_change_ctx into the newly
 introduced struct elevator_resources. The subsequent patch extends the
 struct elevator_resources to include other elevator-related data.

 The third patch introduce ->alloc_sched_data and ->free_sched_data
 elevator ops which could be then used to safely allocate and free
 scheduler data.

 The fourth patch now builds upon the previous patch and starts using
 the newly introduced alloc/free sched data methods in the earlier patch
 during elevator switch and nr_hw_queue update. And while doing so, it's
 ensured that sched data allocation and free happens before we acquire
 ->freeze_lock and ->elevator_lock thus preventing its dependency on
 pcpu_alloc_mutex.

 The last patch of this series converts Kyber scheduler to use the new
 methods inroduced in the previous patch. It hooks Kyber’s scheduler
 data allocation and teardown logic from ->init_sched and ->exit_sched
 into the new methods, ensuring memory operations are performed outside
 locked sections.

 Together, these changes simplify the elevator switch logic and prevent
 the reported lockdep splat."

Link: https://lore.kernel.org/linux-block/20251113090619.2030737-1-nilay@linux.ibm.com/
Signed-off-by: Jens Axboe <axboe@kernel.dk>

* elevator-switch-6.19:
  block: define alloc_sched_data and free_sched_data methods for kyber
  block: use {alloc|free}_sched data methods
  block: introduce alloc_sched_data and free_sched_data elevator methods
  block: move elevator tags into struct elevator_resources
  block: unify elevator tags and type xarrays into struct elv_change_ctx
---

8e1bf774ab18157cb8041628f2661aa12e425914