Re: [PATCH net-next 00/10] net/smc: optimize the parallelism of SMC-R connections

Jan Karcher
2022-08-16T10:17:24Z

On 10.08.2022 19:47, D. Wythe wrote:
> From: "D. Wythe" <alibuda@linux.alibaba.com>
>
> This patch set attempts to optimize the parallelism of SMC-R connections,
> mainly to reduce unnecessary blocking on locks, and to fix exceptions that
> occur after thoses optimization.
>

Thank you again for your submission!
Let me give you a quick update from our side:
We tested your patches on top of the net-next kernel on our s390
systems. They did crash our systems. After verifying our environment we
pulled console logs and now we can tell that there is indeed a problem
with your patches regarding SMC-D. So please do not integrate this
change as of right now. I'm going to do more in depth reviews of your
patches but i need some time for them so here is a quick a description
of the problem:

It is a SMC-D problem, that occurs while building up the connection. In
smc_conn_create you set struct smc_lnk_cluster *lnkc = NULL. For the
SMC-R path you do grab the pointer, for SMC-D that never happens. Still
you are using this refernce for SMC-D => Crash. This problem can be
reproduced using the SMC-D path. Here is an example console output:

[ 779.516382] Unable to handle kernel pointer dereference in virtual
kernel address space
[ 779.516389] Failing address: 0000000000000000 TEID: 0000000000000483
[ 779.516391] Fault in home space mode while using kernel ASCE.
[ 779.516395] AS:0000000069628007 R3:00000000ffbf0007
S:00000000ffbef800 P:000000000000003d
[ 779.516431] Oops: 0004 ilc:2 [#1] SMP
[ 779.516436] Modules linked in: tcp_diag inet_diag ism mlx5_ib
ib_uverbs mlx5_core smc_diag smc ib_core nft_fib_inet nft_fib_ipv4
nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6
nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv
6 nf_defrag_ipv4 ip_set nf_tables n
[ 779.516470] CPU: 0 PID: 24 Comm: kworker/0:1 Not tainted
5.19.0-13940-g22a46254655a #3
[ 779.516476] Hardware name: IBM 8561 T01 701 (z/VM 7.2.0)

[ 779.522738] Workqueue: smc_hs_wq smc_listen_work [smc]
[ 779.522755] Krnl PSW : 0704c00180000000 000003ff803da89c
(smc_conn_create+0x174/0x968 [smc])
[ 779.522766] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:0
PM:0 RI:0 EA:3
[ 779.522770] Krnl GPRS: 0000000000000002 0000000000000000
0000000000000001 0000000000000000
[ 779.522773] 000000008a4128a0 000003ff803f21aa
000000008e30d640 0000000086d72000
[ 779.522776] 0000000086d72000 000000008a412803
000000008a412800 000000008e30d650
[ 779.522779] 0000000080934200 0000000000000000
000003ff803cb954 00000380002dfa88
[ 779.522789] Krnl Code: 000003ff803da88e: e310f0e80024 stg
%r1,232(%r15)
[ 779.522789] 000003ff803da894: a7180000 lhi
%r1,0
[ 779.522789] #000003ff803da898: 582003ac l
%r2,940
[ 779.522789] >000003ff803da89c: ba123020 cs
%r1,%r2,32(%r3)
[ 779.522789] 000003ff803da8a0: ec1603be007e cij
%r1,0,6,000003ff803db01c

[ 779.522789] 000003ff803da8a6: 4110b002 la
%r1,2(%r11)
[ 779.522789] 000003ff803da8aa: e310f0f00024 stg
%r1,240(%r15)
[ 779.522789] 000003ff803da8b0: e310f0c00004 lg
%r1,192(%r15)
[ 779.522870] Call Trace:
[ 779.522873] [<000003ff803da89c>] smc_conn_create+0x174/0x968 [smc]
[ 779.522884] [<000003ff803cb954>]
smc_find_ism_v2_device_serv+0x1b4/0x300 [smc]
01: HCPGSP2629I The virtual machine is placed in CP mode due to a SIGP
stop from CPU 01.
01: HCPGSP2629I The virtual machine is placed in CP mode due to a SIGP
stop from CPU 00.
[ 779.522894] [<000003ff803cbace>] smc_listen_find_device+0x2e/0x370 [smc]

I'm going to send the review for the first patch right away (which is
the one causing the crash), so far I'm done with it. The others are
going to follow. Maybe you can look over the problem and come up with a
solution, otherwise we are going to decide if we want to look into it as
soon as I'm done with the reviews. Thank you for your patience.