Re: [PATCH V2] RDMA/rtrs: Call {get,put}_cpu_ptr to silence a debug kernel warning

[Leon Romanovsky <leon@kernel.org>]

On Sun, Nov 28, 2021 at 09:35:01PM +0800, Guoqing Jiang wrote:
> With preemption enabled (CONFIG_DEBUG_PREEMPT=y), the following appeared
> when rnbd client tries to map remote block device.
> 
> [ 2123.221071] BUG: using smp_processor_id() in preemptible [00000000] code: bash/1733
> [ 2123.221175] caller is debug_smp_processor_id+0x17/0x20
> [ 2123.221214] CPU: 0 PID: 1733 Comm: bash Not tainted 5.16.0-rc1 #5
> [ 2123.221218] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a-rebuilt.opensuse.org 04/01/2014
> [ 2123.221229] Call Trace:
> [ 2123.221231]  <TASK>
> [ 2123.221235]  dump_stack_lvl+0x5d/0x78
> [ 2123.221252]  dump_stack+0x10/0x12
> [ 2123.221257]  check_preemption_disabled+0xe4/0xf0
> [ 2123.221266]  debug_smp_processor_id+0x17/0x20
> [ 2123.221271]  rtrs_clt_update_all_stats+0x3b/0x70 [rtrs_client]
> [ 2123.221285]  rtrs_clt_read_req+0xc3/0x380 [rtrs_client]
> [ 2123.221298]  ? rtrs_clt_init_req+0xe3/0x120 [rtrs_client]
> [ 2123.221321]  rtrs_clt_request+0x1a7/0x320 [rtrs_client]
> [ 2123.221340]  ? 0xffffffffc0ab1000
> [ 2123.221357]  send_usr_msg+0xbf/0x160 [rnbd_client]
> [ 2123.221370]  ? rnbd_clt_put_sess+0x60/0x60 [rnbd_client]
> [ 2123.221377]  ? send_usr_msg+0x160/0x160 [rnbd_client]
> [ 2123.221386]  ? sg_alloc_table+0x27/0xb0
> [ 2123.221395]  ? sg_zero_buffer+0xd0/0xd0
> [ 2123.221407]  send_msg_sess_info+0xe9/0x180 [rnbd_client]
> [ 2123.221413]  ? rnbd_clt_put_sess+0x60/0x60 [rnbd_client]
> [ 2123.221429]  ? blk_mq_alloc_tag_set+0x2ef/0x370
> [ 2123.221447]  rnbd_clt_map_device+0xba8/0xcd0 [rnbd_client]
> [ 2123.221462]  ? send_msg_open+0x200/0x200 [rnbd_client]
> [ 2123.221479]  rnbd_clt_map_device_store+0x3e5/0x620 [rnbd_client
> 
> To supress the calltrace, let's call get_cpu_ptr/put_cpu_ptr pair in
> rtrs_clt_update_rdma_stats to disable preemption when accessing per-cpu
> variable.
> 
> While at it, let's make the similar change in rtrs_clt_update_wc_stats.
> And for rtrs_clt_inc_failover_cnt, though it was only called inside rcu
> section, but it still can be preempted in case CONFIG_PREEMPT_RCU is
> enabled, so change it to {get,put}_cpu_ptr pair either.
> 
> Signed-off-by: Guoqing Jiang <guoqing.jiang@linux.dev>
> ---
> V2: also make the change in rtrs_clt_update_wc_stats and rtrs_clt_inc_failover_cnt
> 
>  drivers/infiniband/ulp/rtrs/rtrs-clt-stats.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 

Thanks,
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>