WARN @lib/refcount.c:128 during hot unplug of I/O adapter.

[Tyrel Datwyler]

On 04/06/2017 03:27 AM, Sachin Sant wrote:
> On a POWER8 LPAR running 4.11.0-rc5, a hot unplug operation on
> any I/O adapter results in the following warning
> 
> This problem has been in the code for some time now. I had first seen this in
> -next tree.
> 
> [  269.589441] rpadlpar_io: slot PHB 72 removed
> [  270.589997] refcount_t: underflow; use-after-free.
> [  270.590019] ------------[ cut here ]------------
> [  270.590025] WARNING: CPU: 5 PID: 3335 at lib/refcount.c:128 refcount_sub_and_test+0xf4/0x110
> [  270.590028] Modules linked in: xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ipt_REJECT nf_reject_ipv4 tun bridge stp llc rpadlpar_io rpaphp kvm_pr kvm ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter dccp_diag dccp tcp_diag udp_diag inet_diag unix_diag af_packet_diag netlink_diag ghash_generic xts gf128mul vmx_crypto tpm_ibmvtpm tpm sg pseries_rng nfsd auth_rpcgss nfs_acl lockd grace sunrpc binfmt_misc ip_tables xfs libcrc32c sr_mod sd_mod cdrom ibmvscsi ibmveth scsi_transport_srp dm_mirror dm_region_hash dm_log dm_mod
> [  270.590076] CPU: 5 PID: 3335 Comm: drmgr Not tainted 4.11.0-rc5 #3
> [  270.590079] task: c0000005d8df8600 task.stack: c0000000fb3a8000
> [  270.590081] NIP: c000000001aa3ca4 LR: c000000001aa3ca0 CTR: 00000000006338e4
> [  270.590084] REGS: c0000000fb3ab8a0 TRAP: 0700   Not tainted  (4.11.0-rc5)
> [  270.590087] MSR: 8000000000029033 <SF,EE,ME,IR,DR,RI,LE>
> [  270.590090]   CR: 22002422  XER: 00000007
> [  270.590093] CFAR: c000000001edaabc SOFTE: 1 
> [  270.590093] GPR00: c000000001aa3ca0 c0000000fb3abb20 c0000000025ea900 0000000000000026 
> [  270.590093] GPR04: c00000077fc4ada0 c00000077fc617b8 00000000000f0c33 0000000000000000 
> [  270.590093] GPR08: 0000000000000000 c00000000227146c 000000077d9e0000 0000000000003ff0 
> [  270.590093] GPR12: 0000000000002200 c00000000e802d00 0000000000000000 0000000000000000 
> [  270.590093] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
> [  270.590093] GPR20: 0000000000000000 000000001001b5a8 0000000010018338 0000000010016650 
> [  270.590093] GPR24: 000000001001b278 c000000776e0fdcc 0000000010016650 0000000000000000 
> [  270.590093] GPR28: c00000077ffea910 c0000000fbf79180 c000000776e0fdc0 c0000000fbf791d8 
> [  270.590126] NIP [c000000001aa3ca4] refcount_sub_and_test+0xf4/0x110
> [  270.590129] LR [c000000001aa3ca0] refcount_sub_and_test+0xf0/0x110
> [  270.590132] Call Trace:
> [  270.590134] [c0000000fb3abb20] [c000000001aa3ca0] refcount_sub_and_test+0xf0/0x110 (unreliable)
> [  270.590139] [c0000000fb3abb80] [c000000001a8221c] kobject_put+0x3c/0xa0
> [  270.590143] [c0000000fb3abbf0] [c000000001d22d34] of_node_put+0x24/0x40
> [  270.590147] [c0000000fb3abc10] [c00000000165c874] ofdt_write+0x204/0x6b0
> [  270.590151] [c0000000fb3abcd0] [c00000000197a220] proc_reg_write+0x80/0xd0
> [  270.590155] [c0000000fb3abd00] [c0000000018de680] __vfs_write+0x40/0x1c0
> [  270.590158] [c0000000fb3abd90] [c0000000018dffd8] vfs_write+0xc8/0x240
> [  270.590162] [c0000000fb3abde0] [c0000000018e1c40] SyS_write+0x60/0x110
> [  270.590165] [c0000000fb3abe30] [c0000000015cb184] system_call+0x38/0xe0
> [  270.590168] Instruction dump:
> [  270.590170] 7863d182 4e800020 7c0802a6 39200001 3d42fff8 3c62ffb1 386371a8 992a0171 
> [  270.590175] f8010010 f821ffa1 48436de1 60000000 <0fe00000> 38210060 38600000 e8010010 
> [  270.590180] ---[ end trace 08c7a2f3c8bead33 ]—
> 
> Have attached the dmesg log from the system. Let me know if any additional
> information is required to help debug this problem.

I remember you mentioning this when the issue was brought up for CPUs. I
assume the case is the same here where the issue is only seen with
adapters that were hot-added after boot (ie. hot-remove of adapter
present at boot doesn't trip the warning)?

-Tyrel

> 
> Thanks
> -Sachin
> 
>