Re: [PATCH] iomap: Address soft lockup in iomap_finish_ioend()
From: Jens Axboe <axboe@kernel.dk>
Date: 2021-12-30 22:27:27
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linux-fsdevel
On 12/30/21 2:25 PM, Trond Myklebust wrote:
On Thu, 2021-12-30 at 13:24 -0800, Jens Axboe wrote:quoted
On 12/30/21 11:35 AM, trondmy@kernel.org wrote:quoted
From: Trond Myklebust <redacted> 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