RDMA/hns: Fix soft lockup during bt pages loop

Driver runs a for-loop when allocating bt pages and mapping them with
buffer pages. When a large buffer (e.g. MR over 100GB) is being allocated,
it may require a considerable loop count. This will lead to soft lockup:

        watchdog: BUG: soft lockup - CPU#27 stuck for 22s!
        ...
        Call trace:
         hem_list_alloc_mid_bt+0x124/0x394 [hns_roce_hw_v2]
         hns_roce_hem_list_request+0xf8/0x160 [hns_roce_hw_v2]
         hns_roce_mtr_create+0x2e4/0x360 [hns_roce_hw_v2]
         alloc_mr_pbl+0xd4/0x17c [hns_roce_hw_v2]
         hns_roce_reg_user_mr+0xf8/0x190 [hns_roce_hw_v2]
         ib_uverbs_reg_mr+0x118/0x290

        watchdog: BUG: soft lockup - CPU#35 stuck for 23s!
        ...
        Call trace:
         hns_roce_hem_list_find_mtt+0x7c/0xb0 [hns_roce_hw_v2]
         mtr_map_bufs+0xc4/0x204 [hns_roce_hw_v2]
         hns_roce_mtr_create+0x31c/0x3c4 [hns_roce_hw_v2]
         alloc_mr_pbl+0xb0/0x160 [hns_roce_hw_v2]
         hns_roce_reg_user_mr+0x108/0x1c0 [hns_roce_hw_v2]
         ib_uverbs_reg_mr+0x120/0x2bc

Add a cond_resched() to fix soft lockup during these loops. In order not
to affect the allocation performance of normal-size buffer, set the loop
count of a 100GB MR as the threshold to call cond_resched().

Fixes: 38389eaa ("RDMA/hns: Add mtr support for mixed multihop addressing")
Signed-off-by: Junxian Huang <huangjunxian6@hisilicon.com>
Link: https://patch.msgid.link/20250311084857.3803665-3-huangjunxian6@hisilicon.com


Signed-off-by: Leon Romanovsky <leon@kernel.org>