[PATCH] iomap: Address soft lockup in iomap_finish_ioend()

[trondmy@kernel.org]

From: Trond Myklebust <trond.myklebust@hammerspace.com>

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().

Suggested-by: Jens Axboe <axboe@kernel.dk>
Fixes: 598ecfbaa742 ("iomap: lift the xfs writeback code to iomap")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
 fs/iomap/buffered-io.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 71a36ae120ee..e39a53923f9d 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1052,9 +1052,11 @@ iomap_finish_ioend(struct iomap_ioend *ioend, int error)
 			next = bio->bi_private;
 
 		/* walk each page on bio, ending page IO on them */
-		bio_for_each_segment_all(bv, bio, iter_all)
+		bio_for_each_segment_all(bv, bio, iter_all) {
 			iomap_finish_page_writeback(inode, bv->bv_page, error,
 					bv->bv_len);
+			cond_resched();
+		}
 		bio_put(bio);
 	}
 	/* The ioend has been freed by bio_put() */
-- 
2.33.1