> On Mar 31, 2022, at 12:15 PM, Trond Myklebust <trondmy@xxxxxxxxxxxxxxx> wrote: > > On Thu, 2022-03-31 at 15:59 +0000, Chuck Lever III wrote: >> >> >>> 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. >> > > Hmm... Here's another thought. What if this were a deferred request > that is being replayed after an upcall to mountd or the idmapper? It > would mean that the synchronous wait in cache_defer_req() failed, so it > is going to be rare, but it could happen on a congested system. > > AFAICS, svc_defer() does _not_ save rqstp->rq_xprt_ctxt, so > svc_deferred_recv() won't restore it either. True, but TCP and UDP both use rq_xprt_ctxt, so wouldn't we have seen this problem before on a socket transport? I need to audit code to see if saving rq_xprt_ctxt in svc_defer() is safe and reasonable to do. Maybe Bruce has a thought. -- Chuck Lever
