On 12/30/21 2:25 PM, Trond Myklebust wrote: > On Thu, 2021-12-30 at 13:24 -0800, Jens Axboe wrote: >> On 12/30/21 11:35 AM, trondmy@xxxxxxxxxx wrote: >>> From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> >>> >>> We're observing the following stack trace using various kernels >>> when >>> running in the Azure cloud. >>> >>> watchdog: BUG: soft lockup - CPU#12 stuck for 23s! >>> [kworker/12:1:3106] >>> Modules linked in: raid0 ipt_MASQUERADE nf_conntrack_netlink >>> xt_addrtype nft_chain_nat nf_nat br_netfilter bridge stp llc ext4 >>> mbcache jbd2 overlay xt_conntrack nf_conntrack nf_defrag_ipv6 >>> nf_defrag_ipv4 nft_counter rpcrdma rdma_ucm xt_owner ib_srpt >>> nft_compat intel_rapl_msr ib_isert intel_rapl_common nf_tables >>> iscsi_target_mod isst_if_mbox_msr isst_if_common nfnetlink >>> target_core_mod nfit ib_iser libnvdimm libiscsi >>> scsi_transport_iscsi ib_umad kvm_intel ib_ipoib rdma_cm iw_cm vfat >>> ib_cm fat kvm irqbypass crct10dif_pclmul crc32_pclmul mlx5_ib >>> ghash_clmulni_intel rapl ib_uverbs ib_core i2c_piix4 pcspkr >>> hyperv_fb hv_balloon hv_utils joydev nfsd auth_rpcgss nfs_acl lockd >>> grace sunrpc ip_tables xfs libcrc32c mlx5_core mlxfw tls pci_hyperv >>> pci_hyperv_intf sd_mod t10_pi sg ata_generic hv_storvsc hv_netvsc >>> scsi_transport_fc hyperv_keyboard hid_hyperv ata_piix libata >>> crc32c_intel hv_vmbus serio_raw fuse >>> CPU: 12 PID: 3106 Comm: kworker/12:1 Not tainted 4.18.0- >>> 305.10.2.el8_4.x86_64 #1 >>> Hardware name: Microsoft Corporation Virtual Machine/Virtual >>> Machine, BIOS 090008 12/07/2018 >>> Workqueue: xfs-conv/md127 xfs_end_io [xfs] >>> RIP: 0010:_raw_spin_unlock_irqrestore+0x11/0x20 >>> Code: 7c ff 48 29 e8 4c 39 e0 76 cf 80 0b 08 eb 8c 90 90 90 90 90 >>> 90 90 90 90 90 0f 1f 44 00 00 e8 e6 db 7e ff 66 90 48 89 f7 57 9d >>> <0f> 1f 44 00 00 c3 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 8b 07 >>> RSP: 0018:ffffac51d26dfd18 EFLAGS: 00000202 ORIG_RAX: >>> ffffffffffffff12 >>> RAX: 0000000000000001 RBX: ffffffff980085a0 RCX: dead000000000200 >>> RDX: ffffac51d3893c40 RSI: 0000000000000202 RDI: 0000000000000202 >>> RBP: 0000000000000202 R08: ffffac51d3893c40 R09: 0000000000000000 >>> R10: 00000000000000b9 R11: 00000000000004b3 R12: 0000000000000a20 >>> R13: ffffd228f3e5a200 R14: ffff963cf7f58d10 R15: ffffd228f3e5a200 >>> FS: 0000000000000000(0000) GS:ffff9625bfb00000(0000) >>> knlGS:0000000000000000 >>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>> CR2: 00007f5035487500 CR3: 0000000432810004 CR4: 00000000003706e0 >>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >>> Call Trace: >>> wake_up_page_bit+0x8a/0x110 >>> iomap_finish_ioend+0xd7/0x1c0 >>> iomap_finish_ioends+0x7f/0xb0 >>> xfs_end_ioend+0x6b/0x100 [xfs] >>> ? xfs_setfilesize_ioend+0x60/0x60 [xfs] >>> xfs_end_io+0xb9/0xe0 [xfs] >>> process_one_work+0x1a7/0x360 >>> worker_thread+0x1fa/0x390 >>> ? create_worker+0x1a0/0x1a0 >>> kthread+0x116/0x130 >>> ? kthread_flush_work_fn+0x10/0x10 >>> ret_from_fork+0x35/0x40 >>> >>> Jens suggested adding a latency-reducing cond_resched() to the loop >>> in >>> iomap_finish_ioends(). >> >> The patch doesn't add it there though, I was suggesting: >> >> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c >> index 71a36ae120ee..4ad2436a936a 100644 >> --- a/fs/iomap/buffered-io.c >> +++ b/fs/iomap/buffered-io.c >> @@ -1078,6 +1078,7 @@ iomap_finish_ioends(struct iomap_ioend *ioend, >> int error) >> ioend = list_first_entry(&tmp, struct iomap_ioend, >> io_list); >> list_del_init(&ioend->io_list); >> iomap_finish_ioend(ioend, error); >> + cond_resched(); >> } >> } >> EXPORT_SYMBOL_GPL(iomap_finish_ioends); >> >> as I don't think you need it once-per-vec. But not sure if you tested >> that variant or not... >> > > Yes, we did test that variant, but were still seeing the soft lockups > on Azure, hence why I moved it into the inner loop. Gotcha - but maybe just outside the vec loop then, after the bio_put()? Once per vec seems excessive, each vec shouldn't take long, but I guess the ioend inlines can be long? -- Jens Axboe
