On 01/21/2018 08:34 PM, Lu Fengqi wrote:
> On Sun, Jan 21, 2018 at 02:08:58PM -0500, Zygo Blaxell wrote:
>> This warning appears during execution of the LOGICAL_INO ioctl and
>> appears to be spurious:
>>
>> ------------[ cut here ]------------
>> WARNING: CPU: 3 PID: 18172 at fs/btrfs/backref.c:1391
>> find_parent_nodes+0xc41/0x14e0
>> Modules linked in: ib_iser rdma_cm iw_cm ib_cm ib_core configfs
>> iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi overlay r8169 ufs qnx4
>> hfsplus hfs minix ntfs vfat msdos fat jfs xfs cpuid rpcsec_gss_krb5 nfsv4
>> nfsv3 nfs fscache algif_skcipher af_alg softdog nfsd auth_rpcgss nfs_acl
>> lockd grace sunrpc bnep cpufreq_userspace cpufreq_powersave
>> cpufreq_conservative nfnetlink_queue nfnetlink_log nfnetlink bluetooth
>> rfkill snd_seq_dummy snd_hrtimer snd_seq_midi snd_seq_oss snd_seq_midi_event
>> snd_rawmidi snd_seq snd_seq_device binfmt_misc fuse nbd xt_REDIRECT
>> nf_nat_redirect ipt_REJECT nf_reject_ipv4 xt_nat xt_conntrack xt_tcpudp
>> nf_log_ipv4 nf_log_common xt_LOG ip6table_nat nf_conntrack_ipv6
>> nf_defrag_ipv6 nf_nat_ipv6 iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4
>> nf_nat_ipv4 nf_nat nf_conntrack
>> ip6table_mangle iptable_mangle ip6table_filter ip6_tables
>> iptable_filter ip_tables x_tables tcp_cubic dummy lp dm_crypt edac_mce_amd
>> edac_core snd_hda_codec_hdmi ppdev kvm_amd kvm irqbypass crct10dif_pclmul
>> crc32_pclmul ghash_clmulni_intel snd_hda_codec_via pcbc amdkfd
>> snd_hda_codec_generic amd_iommu_v2 aesni_intel snd_hda_intel radeon
>> snd_hda_codec aes_x86_64 snd_hda_core snd_hwdep crypto_simd glue_helper sg
>> snd_pcm_oss cryptd input_leds joydev pcspkr serio_raw snd_mixer_oss rtc_cmos
>> snd_pcm parport_pc parport shpchp wmi acpi_cpufreq evdev snd_timer
>> asus_atk0110 k10temp fam15h_power snd soundcore sp5100_tco hid_generic ipv6
>> af_packet crc_ccitt raid10 raid456 async_raid6_recov async_memcpy async_pq
>> async_xor async_tx libcrc32c raid0 multipath linear dm_mod raid1 md_mod
>> ohci_pci ide_pci_generic
>> sr_mod cdrom pdc202xx_new ohci_hcd crc32c_intel atiixp ehci_pci
>> psmouse ide_core i2c_piix4 ehci_hcd xhci_pci mii xhci_hcd [last unloaded:
>> r8169]
>> CPU: 3 PID: 18172 Comm: bees Tainted: G D W L 4.11.9-zb64+ #1
>> Hardware name: System manufacturer System Product Name/M5A78L-M/USB3,
>> BIOS 2101 12/02/2014
>> Call Trace:
>> dump_stack+0x85/0xc2
>> __warn+0xd1/0xf0
>> warn_slowpath_null+0x1d/0x20
>> find_parent_nodes+0xc41/0x14e0
>> __btrfs_find_all_roots+0xad/0x120
>> ? extent_same_check_offsets+0x70/0x70
>> iterate_extent_inodes+0x168/0x300
>> iterate_inodes_from_logical+0x87/0xb0
>> ? iterate_inodes_from_logical+0x87/0xb0
>> ? extent_same_check_offsets+0x70/0x70
>> btrfs_ioctl+0x8ac/0x2820
>> ? lock_acquire+0xc2/0x200
>> do_vfs_ioctl+0x91/0x700
>> ? __fget+0x112/0x200
>> SyS_ioctl+0x79/0x90
>> entry_SYSCALL_64_fastpath+0x23/0xc6
>> RIP: 0033:0x7f727b20be07
>> RSP: 002b:00007f7279f1e018 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
>> RAX: ffffffffffffffda RBX: ffffffff9c0f4d7f RCX: 00007f727b20be07
>> RDX: 00007f7279f1e118 RSI: 00000000c0389424 RDI: 0000000000000003
>> RBP: 0000000000000035 R08: 00007f72581bf340 R09: 0000000000000000
>> R10: 0000000000000020 R11: 0000000000000246 R12: 0000000000000040
>> R13: 00007f725818d230 R14: 00007f7279f1b640 R15: 00007f7258000020
>> ? trace_hardirqs_off_caller+0x1f/0x140
>> ---[ end trace 5de243350f6762c6 ]---
>> ------------[ cut here ]------------
>>
>> ref->count can be below zero under normal conditions (for delayed refs),
>> so there is no need to spam dmesg when it happens.
>>
>
> Added Edmund.
>
> Hi,
>
> I've also encountered the same problem when running the test case
> xfstests/btrfs/004. However, I'm not sure whether the negative ref->count
> is reasonable.
>
> IMO, these functions (such as add_delayed_refs, add_delayed_refs,
> add_delayed_refs, add_missing_keys and resolve_indirect_refs) have been
> executed at this point in time. Hence, these references not only include
> these refs in the memory (delayed) but also include those refs in the disk
> (inline/keyed). I would appreciate it if you could explain to me why the
> reference count can be reduced to less than zero.
It’s not clear to me that a negative count in this case is expected. For
direct refs the code gets the count from the btrfs_shared_data_ref (in
the item) or the ref_mod (in the delayed ref). For the latter it
_should_ convert a negative count to positive when using as a
prelim_ref. An indirect prelim_ref can also be converted from a direct
in which case it uses the count from the indirect.
I haven't seen this previously but will continue to test. Please let me
know of any additional ways to trigger this.
Thanks,
Ed
>
>> On kernel v4.14 this warning occurs 100-1000 times more frequently than
>> on kernels v4.2..v4.12. In the worst case, one test machine had 59020
>> warnings in 24 hours on v4.14.14 compared to 55 on v4.12.14.
>
> According to my bisect result, The frequency of the warning occurrence
> increased to the detectable degree after this patch
> 86d5f9944252 ("btrfs: convert prelimary reference tracking to use rbtrees")
> is committed. I understand that this does not mean that this patch caused
> the problem, but maybe Edmund can give us some help, so I added him to the
> recipient.
>
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