Re: [PATCH RFC net] linux/dim: Fix divide 0 in RDMA DIM.

[Tao Liu <thomas.liu@ucloud.cn>]

Hi, Yamin and Leon. Do you have any comments about this patch?

On Thu, Jun 23, 2022 at 04:58:58PM +0800, Tao Liu wrote:
> We hit a divide 0 error in ofed 5.1.2.3.7.1. But dim.c and
> rdma_dim.c seem same as upstream.
> 
> CallTrace:
>   Hardware name: H3C R4900 G3/RS33M2C9S, BIOS 2.00.37P21 03/12/2020
>   task: ffff880194b78000 task.stack: ffffc90006714000
>   RIP: 0010:backport_rdma_dim+0x10e/0x240 [mlx_compat]
>   RSP: 0018:ffff880c10e83ec0 EFLAGS: 00010202
>   RAX: 0000000000002710 RBX: ffff88096cd7f780 RCX: 0000000000000064
>   RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000001
>   RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
>   R10: 0000000000000000 R11: 0000000000000000 R12: 000000001d7c6c09
>   R13: ffff88096cd7f780 R14: ffff880b174fe800 R15: 0000000000000000
>   FS:  0000000000000000(0000) GS:ffff880c10e80000(0000)
>   knlGS:0000000000000000
>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   CR2: 00000000a0965b00 CR3: 000000000200a003 CR4: 00000000007606e0
>   DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>   DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>   PKRU: 55555554
>   Call Trace:
>    <IRQ>
>    ib_poll_handler+0x43/0x80 [ib_core]
>    irq_poll_softirq+0xae/0x110
>    __do_softirq+0xd1/0x28c
>    irq_exit+0xde/0xf0
>    do_IRQ+0x54/0xe0
>    common_interrupt+0x8f/0x8f
>    </IRQ>
>    ? cpuidle_enter_state+0xd9/0x2a0
>    ? cpuidle_enter_state+0xc7/0x2a0
>    ? do_idle+0x170/0x1d0
>    ? cpu_startup_entry+0x6f/0x80
>    ? start_secondary+0x1b9/0x210
>    ? secondary_startup_64+0xa5/0xb0
>   Code: 0f 87 e1 00 00 00 8b 4c 24 14 44 8b 43 14 89 c8 4d 63 c8 44 29 c0 99 31 d0 29 d0 31 d2 48 98 48 8d 04 80 48 8d 04 80 48 c1 e0 02 <49> f7 f1 48 83 f8 0a 0f 86 c1 00 00 00 44 39 c1 7f 10 48 89 df
>   RIP: backport_rdma_dim+0x10e/0x240 [mlx_compat] RSP: ffff880c10e83ec0
> 
> crash> struct dim ffff88096cd7f780
> struct dim {
>   state = 1 '\001',
>   prev_stats = {
>       ppms = 2142150514,
>       bpms = 391112768,
>       epms = -30709,
>       cpms = 1,
>       cpe_ratio = 0
>     },
>   start_sample = {
>       time = 51174507127193614,
>       pkt_ctr = 0,
>       byte_ctr = 0,
>       event_ctr = 1,
>       comp_ctr = 494693321
>     },
>   measuring_sample = {
>       time = 51174507266581985,
>       pkt_ctr = 0,
>       byte_ctr = 0,
>       event_ctr = 65,
>       comp_ctr = 494693385
>     },
>   work = {
>       data = {
>             counter = 128
>           },
>       entry = {
>             next = 0xffff88096cd7f7d0,
>             prev = 0xffff88096cd7f7d0
>           },
>       func = 0xffffffffa02b9f80
>     },
>   priv = 0xffff880b174fe800,
>   profile_ix = 1 '\001',
>   mode = 0 '\000',
>   tune_state = 2 '\002',
>   steps_right = 1 '\001',
>   steps_left = 1 '\001',
>   tired = 0 '\000'
> }
> 
> Fixes: f4915455dcf0 ("linux/dim: Implement RDMA adaptive moderation (DIM)")
> Signed-off-by: Tao Liu <thomas.liu@ucloud.cn>
> ---
>  lib/dim/rdma_dim.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/lib/dim/rdma_dim.c b/lib/dim/rdma_dim.c
> index 15462d54758d..a657b106343c 100644
> --- a/lib/dim/rdma_dim.c
> +++ b/lib/dim/rdma_dim.c
> @@ -34,6 +34,9 @@ static int rdma_dim_stats_compare(struct dim_stats *curr,
>  		return (curr->cpms > prev->cpms) ? DIM_STATS_BETTER :
>  						DIM_STATS_WORSE;
>  
> +	if (!prev->cpe_ratio)
> +		return DIM_STATS_SAME;
> +
>  	if (IS_SIGNIFICANT_DIFF(curr->cpe_ratio, prev->cpe_ratio))
>  		return (curr->cpe_ratio > prev->cpe_ratio) ? DIM_STATS_BETTER :
>  						DIM_STATS_WORSE;
> -- 
> 2.30.1 (Apple Git-130)
> 
>