Re: [PATCH v2 0/2] blk-mq: use array manage hctx map instead of xarray

[Jens Axboe <axboe@kernel.dk>]

On 11/26/25 6:39 PM, Fengnan Chang wrote:
> From: Fengnan Chang <changfengnan@bytedance.com>
> 
> After commit 4e5cc99e1e48 ("blk-mq: manage hctx map via xarray"), we use
> an xarray instead of array to store hctx, but in poll mode, each time
> in blk_mq_poll, we need use xa_load to find corresponding hctx, this
> introduce some costs. In my test, xa_load may cost 3.8% cpu.
> 
> After revert previous change, eliminates the overhead of xa_load and can
> result in a 3% performance improvement.
> 
> potentital use-after-free on q->queue_hw_ctx can be fixed by use rcu to
> avoid, same as Yu Kuai did in [1].
> 
> [1] https://lore.kernel.org/all/20220225072053.2472431-1-yukuai3@huawei.com/
> 
> Fengnan Chang (2):
>   blk-mq: use array manage hctx map instead of xarray
>   blk-mq: fix potential uaf for 'queue_hw_ctx'
> 
>  block/blk-mq-tag.c     |  2 +-
>  block/blk-mq.c         | 63 ++++++++++++++++++++++++++++--------------
>  block/blk-mq.h         | 13 ++++++++-
>  include/linux/blk-mq.h |  3 +-
>  include/linux/blkdev.h |  2 +-
>  5 files changed, 58 insertions(+), 25 deletions(-)
> 
> 
> base-commit: 4941a17751c99e17422be743c02c923ad706f888

Adding correct Yu address, was also wrong for v1 and somehow not
corrected?

-- 
Jens Axboe