On Mon, May 24, 2021 at 12:04:16PM +0200, Jan Kara wrote:
> Lockdep complains about lock inversion between ioc->lock and bfqd->lock:
>
> bfqd -> ioc:
> put_io_context+0x33/0x90 -> ioc->lock grabbed
> blk_mq_free_request+0x51/0x140
> blk_put_request+0xe/0x10
> blk_attempt_req_merge+0x1d/0x30
> elv_attempt_insert_merge+0x56/0xa0
> blk_mq_sched_try_insert_merge+0x4b/0x60
> bfq_insert_requests+0x9e/0x18c0 -> bfqd->lock grabbed
> blk_mq_sched_insert_requests+0xd6/0x2b0
> blk_mq_flush_plug_list+0x154/0x280
> blk_finish_plug+0x40/0x60
> ext4_writepages+0x696/0x1320
> do_writepages+0x1c/0x80
> __filemap_fdatawrite_range+0xd7/0x120
> sync_file_range+0xac/0xf0
>
> ioc->bfqd:
> bfq_exit_icq+0xa3/0xe0 -> bfqd->lock grabbed
> put_io_context_active+0x78/0xb0 -> ioc->lock grabbed
> exit_io_context+0x48/0x50
> do_exit+0x7e9/0xdd0
> do_group_exit+0x54/0xc0
>
> To avoid this inversion we change blk_mq_sched_try_insert_merge() to not
> free the merged request but rather leave that upto the caller similarly
> to blk_mq_sched_try_merge(). And in bfq_insert_requests() we make sure
> to free all the merged requests after dropping bfqd->lock.
>
> Fixes: aee69d78dec0 ("block, bfq: introduce the BFQ-v0 I/O scheduler as an extra scheduler")
> Signed-off-by: Jan Kara <jack@xxxxxxx>
Looks fine,
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
Thanks,
Ming
