> On Mar 31, 2022, at 11:21 AM, Chuck Lever III <chuck.lever@xxxxxxxxxx> wrote: > > > >> On Mar 31, 2022, at 11:16 AM, Trond Myklebust <trondmy@xxxxxxxxxxxxxxx> wrote: >> >> Hi Chuck, >> >> >> I'm seeing a very weird stack trace on one of our systems: >> >> [88463.974603] BUG: kernel NULL pointer dereference, address: 0000000000000058 >> [88463.974778] #PF: supervisor read access in kernel mode >> [88463.974916] #PF: error_code(0x0000) - not-present page >> [88463.975037] PGD 0 P4D 0 >> [88463.975164] Oops: 0000 [#1] SMP NOPTI >> [88463.975296] CPU: 4 PID: 12597 Comm: nfsd Kdump: loaded Not tainted 5.15.31-200.pd.17802.el7.x86_64 #1 >> [88463.975452] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 12/12/2018 >> [88463.975630] RIP: 0010:svc_rdma_sendto+0x26/0x330 [rpcrdma] >> [88463.975831] Code: 1f 44 00 00 0f 1f 44 00 00 41 57 41 56 41 55 41 54 55 53 48 83 ec 28 4c 8b 6f 20 4c 8b a7 90 01 00 00 48 89 3c 24 49 8b 45 38 <49> 8b 5c 24 58 a8 40 0f 85 f8 01 00 00 49 8b 45 38 a8 04 0f 85 ec >> [88463.976247] RSP: 0018:ffffad54c20b3e80 EFLAGS: 00010282 >> [88463.976469] RAX: 0000000000004119 RBX: ffff94557ccd8400 RCX: ffff9455daf0c000 >> [88463.976705] RDX: ffff9455daf0c000 RSI: ffff9455da8601a8 RDI: ffff9455da860000 >> [88463.976946] RBP: ffff9455da860000 R08: ffff945586b6b388 R09: ffff945586b6b388 >> [88463.977196] R10: 7f0f1dac00000002 R11: 0000000000000000 R12: 0000000000000000 >> [88463.977449] R13: ffff945663080800 R14: ffff9455da860000 R15: ffff9455dabb8000 >> [88463.977709] FS: 0000000000000000(0000) GS:ffff94586fd00000(0000) knlGS:0000000000000000 >> [88463.977982] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> [88463.978254] CR2: 0000000000000058 CR3: 00000001f9282006 CR4: 00000000003706e0 >> [88463.978583] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >> [88463.978865] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >> [88463.979141] Call Trace: >> [88463.979419] <TASK> >> [88463.979693] ? svc_process_common+0xfa/0x6a0 [sunrpc] >> [88463.980021] ? svc_rdma_cma_handler+0x30/0x30 [rpcrdma] >> [88463.980320] ? svc_recv+0x48a/0x8c0 [sunrpc] >> [88463.980662] svc_send+0x49/0x120 [sunrpc] >> [88463.981009] nfsd+0xe8/0x140 [nfsd] >> [88463.981346] ? nfsd_shutdown_threads+0x80/0x80 [nfsd] >> [88463.981675] kthread+0x127/0x150 >> [88463.981981] ? set_kthread_struct+0x40/0x40 >> [88463.982284] ret_from_fork+0x22/0x30 >> [88463.982586] </TASK> >> [88463.982886] Modules linked in: nfsv3 bpf_preload xt_nat veth nfs_layout_flexfiles auth_name rpcsec_gss_krb5 nfsv4 dns_resolver nfsidmap nfs nfsd auth_rpcgss nfs_acl lockd grace xt_MASQUERADE nf_conntrack_netlink xt_addrtype br_netfilter bridge stp llc overlay nf_nat_ftp nf_conntrack_netbios_ns nf_conntrack_broadcast nf_conntrack_ftp xt_CT xt_sctp ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 xt_conntrack ip6table_nat ip6table_mangle ip6table_security ip6table_raw iptable_nat nf_nat iptable_mangle iptable_security iptable_raw nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip_set nfnetlink ip6table_filter ip6_tables iptable_filter vsock_loopback vmw_vsock_virtio_transport_common vmw_vsock_vmci_transport vsock bonding ipmi_msghandler vfat fat rpcrdma sunrpc rdma_ucm ib_iser libiscsi scsi_transport_iscsi ib_umad rdma_cm iw_cm ib_ipoib ib_cm intel_rapl_msr intel_rapl_common crct10dif_pclmul mlx5_ib crc32_pclmul ghash_clmulni_intel rapl ib_uverbs ib_core vmw_vmci i2c_piix4 >> [88463.982930] dm_multipath ip_tables xfs mlx5_core crc32c_intel ttm vmxnet3 vmw_pvscsi drm_kms_helper mlxfw cec pci_hyperv_intf tls ata_generic drm pata_acpi psample >> >> Decoding the address svc_rdma_sendto+0x26 resolves to line 927 in >> net/sunrpc/xprtrdma/svc_rdma_sendto.c >> >> i.e. >> >> 927 __be32 *rdma_argp = rctxt->rc_recv_buf; >> >> which shows that somehow, we're getting to svc_rdma_sendto() with a >> request that has rqstp->rq_xprt_ctxt == NULL. >> >> I'm having trouble seeing how that can happen, but thought I'd ask in >> case you've seen something similar. AFAICS, the code in that area has >> not changed since early 2021. >> >> As I understand it, knfsd was in the process of shutting down at the >> time, so it is possible there is a connection to that... > > My immediate response is "that's not supposed to happen". I'll give > it some thought, but yeah, I bet the transport sendto code is not > dealing with connection shutdown properly. I still don't see exactly how @rctxt could be NULL here, but it might be enough to move the deref of @rctxt down past the svc_xprt_is_dead() test, say just before "*p++ = *rdma_argp;". In any event, it could be that recent reorganization of generic transport code might be responsible, or maybe that this is just a hard race to hit. -- Chuck Lever
