Hi,

We have a user reporting BUG splats and FSCache assertion failures with
FSCache and NFS. The full stack traces are below.

We are consistently seeing the following FSCache assertion:

[81738.886634] FS-Cache: 
[81738.888281] FS-Cache: Assertion failed
[81738.889461] FS-Cache: 6 == 5 is false
[81738.890625] ------------[ cut here ]------------
[81738.891706] kernel BUG at 
/build/linux-hVVhWi/linux-4.4.0/fs/fscache/operation.c:494!

which references the following:

        ASSERTIFCMP(op->state != FSCACHE_OP_ST_INITIALISED &&
                    op->state != FSCACHE_OP_ST_COMPLETE,
                    op->state, ==, FSCACHE_OP_ST_CANCELLED);

So the operation has become DEAD when it was expected to be CANCELLED.

fscache_put_operation() is the only thing I can find that will mark an
operation as DEAD, and then only when atomic_dec_and_test(&op->usage)
goes to 0 twice.

This looks supsiciously like this bug reported in June 2017:
https://www.redhat.com/archives/linux-cachefs/2017-June/msg00002.html
"Re: [Linux-cachefs] Problem: Race in fscache operation enqueuing for
reading and copying multiple pages from cachefiles to netfs causes
kernel oops or at worst memory scribbling."

Indeed, immediatlely prior to the assertion failure, we sometimes see a
WARN in the workqueue code from trying to insert a work that is not
pending, and the stack trace includes cachefiles_read_waiter calling
fscache_enqueue_operation.

Was there ever any progress on that bug? Or is there anything else I
should be looking at?

Thanks in advance!

Regards,
Daniel


Full stack traces:

[81738.885081] ------------[ cut here ]------------
[81738.885165] WARNING: CPU: 67 PID: 70869 at 
/build/linux-hVVhWi/linux-4.4.0/kernel/workqueue.c:623 insert_work+0xac/0xc0()
[81738.885175] Modules linked in: binfmt_misc veth ipt_MASQUERADE 
nf_nat_masquerade_ipv4 nf_conntrack_netlink nfnetlink xfrm_user xfrm_algo 
iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 xt_addrtype 
xt_conntrack nf_nat nf_conntrack br_netfilter bridge stp llc overlay 
xt_multiport iptable_filter ip_tables x_tables nfsv3 nfs_acl rpcsec_gss_krb5 
auth_rpcgss nfsv4 nfs lockd grace nv_peer_mem(OE) cachefiles fscache msr 
rdma_ucm(OE) ib_ucm(OE) rdma_cm(OE) iw_cm(OE) configfs ib_ipoib(OE) ib_cm(OE) 
ib_uverbs(OE) ib_umad(OE) mlx5_ib(OE) mlx4_ib(OE) ib_core(OE) mlx4_en(OE) 
mlx4_core(OE) bonding ipmi_ssif intel_rapl x86_pkg_temp_thermal 
intel_powerclamp coretemp kvm_intel kvm irqbypass crct10dif_pclmul crc32_pclmul 
ghash_clmulni_intel aesni_intel aes_x86_64 lrw gf128mul glue_helper ablk_helper 
cryptd joydev input_leds mxm_wmi sb_edac edac_core lpc_ich mei_me mei 
nvidia_uvm(POE) shpchp 8250_fintek ipmi_si wmi acpi_power_meter mac_hid sunrpc 
ipmi_devintf ipmi_msghandler knem(OE) autofs4
  nvidia_drm(POE) nvidia_modeset(POE) ast i2c_algo_bit nvidia(POE) ttm ixgbe 
drm_kms_helper syscopyarea ses dca sysfillrect mlx5_core(OE) enclosure 
sysimgblt fb_sys_fops vxlan hid_generic ip6_udp_tunnel usbhid udp_tunnel 
mlx_compat(OE) hid ahci ptp megaraid_sas drm libahci pps_core mdio fjes
[81738.885422] CPU: 67 PID: 70869 Comm: xxxxxx Tainted: P           OE   
4.4.0-92-generic #115-Ubuntu
[81738.885428] Hardware name: xxxxx
[81738.885431]  0000000000000086 6bb3b89857e8c7df ffff887f7f2c3b60 
ffffffff813f9c83
[81738.885436]  0000000000000000 ffffffff81cbb498 ffff887f7f2c3b98 
ffffffff81081312
[81738.885439]  ffff887f22fdd200 ffff887f626bc540 ffff887f656e8000 
0000000000000005
[81738.885446] Call Trace:
[81738.885452]  <IRQ>  [<ffffffff813f9c83>] dump_stack+0x63/0x90
[81738.885512]  [<ffffffff81081312>] warn_slowpath_common+0x82/0xc0
[81738.885535]  [<ffffffff8108145a>] warn_slowpath_null+0x1a/0x20
[81738.885558]  [<ffffffff8109869c>] insert_work+0xac/0xc0
[81738.885571]  [<ffffffff810987e9>] __queue_work+0x139/0x3b0
[81738.885579]  [<ffffffff81098c77>] queue_work_on+0x27/0x40
[81738.885625]  [<ffffffffc054b064>] fscache_enqueue_operation+0x94/0x150 
[fscache]
[81738.885640]  [<ffffffffc03b68ec>] cachefiles_read_waiter+0xbc/0x100 
[cachefiles]
[81738.885666]  [<ffffffff810c3d12>] __wake_up_common+0x52/0x90
[81738.885694]  [<ffffffff810c3d89>] __wake_up+0x39/0x50
[81738.885715]  [<ffffffff810c4040>] __wake_up_bit+0x50/0x70
[81738.885726]  [<ffffffff8118f739>] unlock_page+0x69/0x70
[81738.885746]  [<ffffffff812e8073>] mpage_end_io+0x33/0xc0
[81738.885770]  [<ffffffff813c28af>] bio_endio+0x3f/0x60
[81738.885782]  [<ffffffff813ca257>] blk_update_request+0x87/0x310
[81738.885801]  [<ffffffff815c40b3>] scsi_end_request+0x33/0x1d0
[81738.885815]  [<ffffffff815c77e6>] scsi_io_completion+0x1b6/0x690
[81738.885841]  [<ffffffff815be40f>] scsi_finish_command+0xcf/0x120
[81738.885858]  [<ffffffff815c6f74>] scsi_softirq_done+0x124/0x150
[81738.885897]  [<ffffffff813d2147>] blk_done_softirq+0x87/0xb0
[81738.885916]  [<ffffffff81085df1>] __do_softirq+0x101/0x290
[81738.885933]  [<ffffffff810860f3>] irq_exit+0xa3/0xb0
[81738.885950]  [<ffffffff818449e4>] do_IRQ+0x54/0xd0
[81738.885975]  [<ffffffff81842ac2>] common_interrupt+0x82/0x82
[81738.885982]  <EOI>  [<ffffffff811fe87c>] ? try_charge+0x3c/0x660
[81738.886035]  [<ffffffff810c4125>] ? wake_up_bit+0x25/0x30
[81738.886057]  [<ffffffff81202ceb>] mem_cgroup_try_charge+0x6b/0x1e0
[81738.886074]  [<ffffffff8118fc40>] __add_to_page_cache_locked+0x60/0x1f0
[81738.886194]  [<ffffffffc141cd83>] ? nfs_pageio_add_request+0xa3/0x1b0 [nfs]
[81738.886284]  [<ffffffffc141d760>] ? nfs_read_completion+0x210/0x210 [nfs]
[81738.886299]  [<ffffffff8118fe27>] add_to_page_cache_lru+0x37/0x90
[81738.886316]  [<ffffffff8119df5b>] read_cache_pages+0x7b/0x120
[81738.886401]  [<ffffffffc141de79>] nfs_readpages+0x129/0x200 [nfs]
[81738.886429]  [<ffffffff8119e1e6>] __do_page_cache_readahead+0x196/0x230
[81738.886454]  [<ffffffff8119e3bd>] ondemand_readahead+0x13d/0x250
[81738.886469]  [<ffffffff8119e53b>] page_cache_async_readahead+0x6b/0x70
[81738.886478]  [<ffffffff81190dd8>] generic_file_read_iter+0x458/0x670
[81738.886529]  [<ffffffffc1415292>] ? __nfs_revalidate_mapping+0xc2/0x280 [nfs]
[81738.886564]  [<ffffffffc1410c72>] nfs_file_read+0x52/0xa0 [nfs]
[81738.886577]  [<ffffffff8120eec4>] new_sync_read+0x94/0xd0
[81738.886584]  [<ffffffff8120ef26>] __vfs_read+0x26/0x40
[81738.886589]  [<ffffffff8120f4e6>] vfs_read+0x86/0x130
[81738.886595]  [<ffffffff81210235>] SyS_read+0x55/0xc0
[81738.886606]  [<ffffffff81841ff2>] entry_SYSCALL_64_fastpath+0x16/0x71
[81738.886612] ---[ end trace dbbc7c60b0e5f2a3 ]---

[81738.886634] FS-Cache: 
[81738.888281] FS-Cache: Assertion failed
[81738.889461] FS-Cache: 6 == 5 is false
[81738.890625] ------------[ cut here ]------------
[81738.891706] kernel BUG at 
/build/linux-hVVhWi/linux-4.4.0/fs/fscache/operation.c:494!
[81738.892821] invalid opcode: 0000 [#1] SMP 
[81738.893930] Modules linked in: binfmt_misc veth ipt_MASQUERADE 
nf_nat_masquerade_ipv4 nf_conntrack_netlink nfnetlink xfrm_user xfrm_algo 
iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 xt_addrtype 
xt_conntrack nf_nat nf_conntrack br_netfilter bridge stp llc overlay 
xt_multiport iptable_filter ip_tables x_tables nfsv3 nfs_acl rpcsec_gss_krb5 
auth_rpcgss nfsv4 nfs lockd grace nv_peer_mem(OE) cachefiles fscache msr 
rdma_ucm(OE) ib_ucm(OE) rdma_cm(OE) iw_cm(OE) configfs ib_ipoib(OE) ib_cm(OE) 
ib_uverbs(OE) ib_umad(OE) mlx5_ib(OE) mlx4_ib(OE) ib_core(OE) mlx4_en(OE) 
mlx4_core(OE) bonding ipmi_ssif intel_rapl x86_pkg_temp_thermal 
intel_powerclamp coretemp kvm_intel kvm irqbypass crct10dif_pclmul crc32_pclmul 
ghash_clmulni_intel aesni_intel aes_x86_64 lrw gf128mul glue_helper ablk_helper 
cryptd joydev input_leds mxm_wmi sb_edac edac_core lpc_ich mei_me mei 
nvidia_uvm(POE) shpchp 8250_fintek ipmi_si wmi acpi_power_meter mac_hid sunrpc 
ipmi_devintf ipmi_msghandler knem(OE) autofs4
  nvidia_drm(POE) nvidia_modeset(POE) ast i2c_algo_bit nvidia(POE) ttm ixgbe 
drm_kms_helper syscopyarea ses dca sysfillrect mlx5_core(OE) enclosure 
sysimgblt fb_sys_fops vxlan hid_generic ip6_udp_tunnel usbhid udp_tunnel 
mlx_compat(OE) hid ahci ptp megaraid_sas drm libahci pps_core mdio fjes
[81738.908228] CPU: 23 PID: 36247 Comm: kworker/u162:0 Tainted: P        W  OE  
 4.4.0-92-generic #115-Ubuntu
[81738.910190] Hardware name: xxxxx
[81738.912691] Workqueue: fscache_operation fscache_op_work_func [fscache]
[81738.914032] task: ffff8846c0f23800 ti: ffff886cf2f0c000 task.ti: 
ffff886cf2f0c000
[81738.914880] RIP: 0010:[<ffffffffc054af96>]  [<ffffffffc054af96>] 
fscache_put_operation+0x1d6/0x210 [fscache]
[81738.915788] RSP: 0000:ffff886cf2f0fde0  EFLAGS: 00010282
[81738.916700] RAX: 0000000000000019 RBX: ffff887f626bc540 RCX: 0000000000000006
[81738.917635] RDX: 0000000000000000 RSI: 0000000000000246 RDI: ffff887f7eccdd50
[81738.918571] RBP: ffff886cf2f0fdf8 R08: 0000000000000000 R09: 000000000000079e
[81738.919539] R10: 0000000000000002 R11: 000000000000079e R12: ffff887f656e8000
[81738.920454] R13: ffff887f22fdd200 R14: 0000000000001440 R15: ffff887f626bc540
[81738.921275] FS:  0000000000000000(0000) GS:ffff887f7ecc0000(0000) 
knlGS:0000000000000000
[81738.922089] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[81738.922922] CR2: 00007ff2cce7e880 CR3: 0000000002e0a000 CR4: 00000000003406e0
[81738.923765] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[81738.924650] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[81738.925517] Stack:
[81738.926320]  ffff887f626bc540 ffff887f656e8000 ffff887f22fdd200 
ffff886cf2f0fe10
[81738.927155]  ffffffffc054b1ca ffff887f608c3ec0 ffff886cf2f0fe50 
ffffffff8109a625
[81738.928059]  0000000000000000 ffff887f608c3ef0 ffff887f656e8000 
0000000000000088
[81738.928961] Call Trace:
[81738.929825]  [<ffffffffc054b1ca>] fscache_op_work_func+0x2a/0x50 [fscache]
[81738.930680]  [<ffffffff8109a625>] process_one_work+0x165/0x480
[81738.931547]  [<ffffffff8109a98b>] worker_thread+0x4b/0x4c0
[81738.932427]  [<ffffffff8109a940>] ? process_one_work+0x480/0x480
[81738.933506]  [<ffffffff810a0cc5>] kthread+0xe5/0x100
[81738.934498]  [<ffffffff810a0be0>] ? kthread_create_on_node+0x1e0/0x1e0
[81738.935551]  [<ffffffff8184238f>] ret_from_fork+0x3f/0x70
[81738.936519]  [<ffffffff810a0be0>] ? kthread_create_on_node+0x1e0/0x1e0
[81738.937372] Code: c7 c7 fb 02 55 c0 e8 e1 2b c4 c0 48 c7 c7 09 03 55 c0 e8 
d5 2b c4 c0 8b 73 40 ba 05 00 00 00 48 c7 c7 b0 ee 54 c0 e8 c1 2b c4 c0 <0f> 0b 
48 c7 c7 fb 02 55 c0 e8 b3 2b c4 c0 48 c7 c7 09 03 55 c0 
[81738.939258] RIP  [<ffffffffc054af96>] fscache_put_operation+0x1d6/0x210 
[fscache]
[81738.940185]  RSP <ffff886cf2f0fde0>
[81738.944238] ---[ end trace dbbc7c60b0e5f2a4 ]---

(this usually follows, it just looks like a cascading failure from
messing with the work queue data structures)

[81738.946803] BUG: unable to handle kernel paging request at ffffffffffffffd8
[81738.947768] IP: [<ffffffff810a1370>] kthread_data+0x10/0x20
[81738.948624] PGD 2e0d067 PUD 2e0f067 PMD 0 
[81738.949445] Oops: 0000 [#2] SMP 
[81738.950237] Modules linked in: binfmt_misc veth ipt_MASQUERADE 
nf_nat_masquerade_ipv4 nf_conntrack_netlink nfnetlink xfrm_user xfrm_algo 
iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 xt_addrtype 
xt_conntrack nf_nat nf_conntrack br_netfilter bridge stp llc overlay 
xt_multiport iptable_filter ip_tables x_tables nfsv3 nfs_acl rpcsec_gss_krb5 
auth_rpcgss nfsv4 nfs lockd grace nv_peer_mem(OE) cachefiles fscache msr 
rdma_ucm(OE) ib_ucm(OE) rdma_cm(OE) iw_cm(OE) configfs ib_ipoib(OE) ib_cm(OE) 
ib_uverbs(OE) ib_umad(OE) mlx5_ib(OE) mlx4_ib(OE) ib_core(OE) mlx4_en(OE) 
mlx4_core(OE) bonding ipmi_ssif intel_rapl x86_pkg_temp_thermal 
intel_powerclamp coretemp kvm_intel kvm irqbypass crct10dif_pclmul crc32_pclmul 
ghash_clmulni_intel aesni_intel aes_x86_64 lrw gf128mul glue_helper ablk_helper 
cryptd joydev input_leds mxm_wmi sb_edac edac_core lpc_ich mei_me mei 
nvidia_uvm(POE) shpchp 8250_fintek ipmi_si wmi acpi_power_meter mac_hid sunrpc 
ipmi_devintf ipmi_msghandler knem(OE) autofs4
  nvidia_drm(POE) nvidia_modeset(POE) ast i2c_algo_bit nvidia(POE) ttm ixgbe 
drm_kms_helper syscopyarea ses dca sysfillrect mlx5_core(OE) enclosure 
sysimgblt fb_sys_fops vxlan hid_generic ip6_udp_tunnel usbhid udp_tunnel 
mlx_compat(OE) hid ahci ptp megaraid_sas drm libahci pps_core mdio fjes
[81738.959336] CPU: 23 PID: 36247 Comm: kworker/u162:0 Tainted: P      D W  OE  
 4.4.0-92-generic #115-Ubuntu
[81738.960164] Hardware name: xxxxx
[81738.960993] task: ffff8846c0f23800 ti: ffff886cf2f0c000 task.ti: 
ffff886cf2f0c000
[81738.961808] RIP: 0010:[<ffffffff810a1370>]  [<ffffffff810a1370>] 
kthread_data+0x10/0x20
[81738.962644] RSP: 0000:ffff886cf2f0fab8  EFLAGS: 00010002
[81738.963475] RAX: 0000000000000000 RBX: 0000000000000017 RCX: ffffffff82109e80
[81738.964312] RDX: 0000000000000017 RSI: 0000000000000017 RDI: ffff8846c0f23800
[81738.965142] RBP: ffff886cf2f0fab8 R08: 00000000ffffffff R09: 0000000000000000
[81738.965996] R10: ffff8846c0f23860 R11: 0000000000009800 R12: 0000000000000000
[81738.966825] R13: 0000000000016dc0 R14: ffff8846c0f23800 R15: ffff887f7ecd6dc0
[81738.967676] FS:  0000000000000000(0000) GS:ffff887f7ecc0000(0000) 
knlGS:0000000000000000
[81738.968534] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[81738.969369] CR2: 0000000000000028 CR3: 0000000002e0a000 CR4: 00000000003406e0
[81738.970202] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[81738.971053] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[81738.971893] Stack:
[81738.972728]  ffff886cf2f0fad0 ffffffff8109b9c1 ffff887f7ecd6dc0 
ffff886cf2f0fb20
[81738.973583]  ffffffff8183dab0 ffff887f5f808aa0 ffff886c00000017 
ffff8846c0f23800
[81738.974448]  ffff886cf2f10000 ffff8846c0f23ed0 ffff886cf2f0f6d0 
0000000000000000
[81738.975289] Call Trace:
[81738.976164]  [<ffffffff8109b9c1>] wq_worker_sleeping+0x11/0x90
[81738.977019]  [<ffffffff8183dab0>] __schedule+0x650/0xa30
[81738.977844]  [<ffffffff8183dec5>] schedule+0x35/0x80
[81738.978668]  [<ffffffff81084465>] do_exit+0x775/0xb00
[81738.979484]  [<ffffffff81031c41>] oops_end+0xa1/0xd0
[81738.980294]  [<ffffffff810320fb>] die+0x4b/0x70
[81738.981091]  [<ffffffff8102f121>] do_trap+0xb1/0x140
[81738.981882]  [<ffffffff8102f4a9>] do_error_trap+0x89/0x110
[81738.982656]  [<ffffffffc054af96>] ? fscache_put_operation+0x1d6/0x210 
[fscache]
[81738.983428]  [<ffffffff810ca782>] ? up+0x32/0x50
[81738.984189]  [<ffffffff810d8656>] ? console_unlock+0x216/0x550
[81738.984934]  [<ffffffff8102fa10>] do_invalid_op+0x20/0x30
[81738.985677]  [<ffffffff81843b0e>] invalid_op+0x1e/0x30
[81738.986416]  [<ffffffffc054af96>] ? fscache_put_operation+0x1d6/0x210 
[fscache]
[81738.987155]  [<ffffffffc054b1ca>] fscache_op_work_func+0x2a/0x50 [fscache]
[81738.987890]  [<ffffffff8109a625>] process_one_work+0x165/0x480
[81738.988631]  [<ffffffff8109a98b>] worker_thread+0x4b/0x4c0
[81738.989349]  [<ffffffff8109a940>] ? process_one_work+0x480/0x480
[81738.990049]  [<ffffffff810a0cc5>] kthread+0xe5/0x100
[81738.990724]  [<ffffffff810a0be0>] ? kthread_create_on_node+0x1e0/0x1e0
[81738.991390]  [<ffffffff8184238f>] ret_from_fork+0x3f/0x70
[81738.992042]  [<ffffffff810a0be0>] ? kthread_create_on_node+0x1e0/0x1e0
[81738.992671] Code: ff ff ff be 49 02 00 00 48 c7 c7 98 b9 cb 81 e8 e7 00 fe 
ff e9 a6 fe ff ff 66 90 0f 1f 44 00 00 48 8b 87 18 05 00 00 55 48 89 e5 <48> 8b 
40 d8 5d c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 
[81738.994013] RIP  [<ffffffff810a1370>] kthread_data+0x10/0x20
[81738.994627]  RSP <ffff886cf2f0fab8>
[81738.995216] CR2: ffffffffffffffd8
[81738.995785] ---[ end trace dbbc7c60b0e5f2a5 ]---
[81738.997887] Fixing recursive fault but reboot is needed!

(hardlockups seem to follow)

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