Hi Jens,
I believe this patchset may have fallen through the cracks. I've just rebased it on
top of the block-6.17 branch at commit 5421681bc3ef ("blk-ioc: don't hold queue_lock
for ioc_lookup_icq()") and sent out v8.
Could you please consider pulling it for Linux 6.17?
Thanks!
--Nilay
On 7/30/25 1:16 PM, Nilay Shroff wrote:
> Hi,
>
> There have been a few reports[1] indicating potential lockdep warnings due
> to a lock dependency from the percpu allocator to the elevator lock. This
> patch series aims to eliminate that dependency.
>
> The series consists of three patches:
> The first patch is preparatory patch and just move elevator queue
> allocation logic from ->init_sched into blk_mq_init_sched.
>
> The second patch in the series restructures sched_tags allocation and
> deallocation during elevator update/switch operations to ensure these
> actions are performed entirely outside the ->freeze_lock and ->elevator_
> lock. This eliminates the percpu allocator’s lock dependency on the
> elevator and freeze lock during scheduler transitions.
>
> The third patch introduces batch allocation and deallocation helpers for
> sched_tags. These helpers are used during __blk_mq_update_nr_hw_queues()
> to decouple sched_tags memory management from both the elevator and freeze
> locks, addressing the lockdep concerns in the nr_hw_queues update path.
>
> [1] https://lore.kernel.org/all/0659ea8d-a463-47c8-9180-43c719e106eb@xxxxxxxxxxxxx/
>
> Changes since v7:
> - Rebased code on top of block-6.17, commit 5421681bc3ef ("blk-ioc: don't
> hold queue_lock for ioc_lookup_icq()")
> Link to v7: https://lore.kernel.org/all/20250701081954.57381-1-nilay@xxxxxxxxxxxxx/
>
> Changes since v6:
> - Add warning when loading elevator tags from an xarray yields nothing
> (Hannes Reinecke)
> - Use elevator tags instead of xarray table as a function argument to
> elv_update_nr_hw_queues (Ming Lei)
> Link to v6: https://lore.kernel.org/all/20250630054756.54532-1-nilay@xxxxxxxxxxxxx/
>
> Changes since v5:
> - Fixed smatch warning reported by kernel test robot here:
> https://lore.kernel.org/all/202506300509.2S1tygch-lkp@xxxxxxxxx/
> Link to v5: https://lore.kernel.org/all/20250627175544.1063910-1-nilay@xxxxxxxxxxxxx/
>
> Changes since v4:
> - Define a local Xarray variable in __blk_mq_update_nr_hw_queues to store
> sched_tags, instead of storing it in an Xarray defined in 'struct elevator_tags'
> (Ming Lei)
> Link to v4: https://lore.kernel.org/all/20250624131716.630465-1-nilay@xxxxxxxxxxxxx/
>
> Changes since v3:
> - Further split the patchset into three patch series so that we can
> have a separate patch for sched_tags batch allocation/deallocation
> (Ming Lei)
> - Use Xarray to store and load the sched_tags (Ming Lei)
> - Unexport elevator_alloc() as we no longer need to use it outside
> of block layer core (hch)
> - unwind the sched_tags allocation and free tags when we it fails in
> the middle of allocation (hch)
> - Move struct elevator_queue header from commin header to elevator.c
> as there's no user of it outside elevator.c (Ming Lei, hch)
> Link to v3: https://lore.kernel.org/all/20250616173233.3803824-1-nilay@xxxxxxxxxxxxx/
>
> Change since v2:
> - Split the patch into a two patch series. The first patch updates
> ->init_sched elevator API change and second patch handles the sched
> tags allocation/de-allocation logic (Ming Lei)
> - Address sched tags allocation/deallocation logic while running in the
> context of nr_hw_queue update so that we can handle all possible
> scenarios in a single patchest (Ming Lei)
> Link to v2: https://lore.kernel.org/all/20250528123638.1029700-1-nilay@xxxxxxxxxxxxx/
>
> Changes since v1:
> - As the lifetime of elevator queue and sched tags are same, allocate
> and move sched tags under struct elevator_queue (Ming Lei)
> Link to v1: https://lore.kernel.org/all/20250520103425.1259712-1-nilay@xxxxxxxxxxxxx/
>
> Nilay Shroff (3):
> block: move elevator queue allocation logic into blk_mq_init_sched
> block: fix lockdep warning caused by lock dependency in
> elv_iosched_store
> block: fix potential deadlock while running nr_hw_queue update
>
> block/bfq-iosched.c | 13 +--
> block/blk-mq-sched.c | 223 ++++++++++++++++++++++++++++--------------
> block/blk-mq-sched.h | 12 ++-
> block/blk-mq.c | 16 ++-
> block/blk.h | 4 +-
> block/elevator.c | 38 +++++--
> block/elevator.h | 16 ++-
> block/kyber-iosched.c | 11 +--
> block/mq-deadline.c | 14 +--
> 9 files changed, 228 insertions(+), 119 deletions(-)
>
