On 23.01.2018 05:35, Edmund Nadolski wrote:
> On 1/22/18 5:58 AM, Nikolay Borisov wrote:
>>
>>
>> On 21.01.2018 21:08, 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.
>>
>> Why do you think it's normal for this to be a negative value under
>> normal conditions? There should be some rationale about that otherwise
>> you are pampering over a bug.
>
>
> The ref->count in the prelim_ref can be <0 for a delayed ref that
> has a node->action of BTRFS_DROP_DELAYED_REF. The prelim_ref_insert()
> relies on this when merging identical refs to keep the overall
> count correct. So it looks to me like it should be OK to remove
> the WARN.
Right, I don't understand the backref code so I will have to agree with
you :) At least the explanation you provided should be in the change log
>
> (However the ref_mod in the btrfs_delayed_ref_node evidently cannot
> go <0).
>
>
>>> 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.
>>>
>>> Signed-off-by: Zygo Blaxell <ce3g8...@umail.furryterror.org>
>>> ---
>>> fs/btrfs/backref.c | 1 -
>>> 1 file changed, 1 deletion(-)
>>>
>>> diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
>>> index 7d0dc100a09a..57e8d2562ed5 100644
>>> --- a/fs/btrfs/backref.c
>>> +++ b/fs/btrfs/backref.c
>>> @@ -1263,7 +1263,6 @@ static int find_parent_nodes(struct
>>> btrfs_trans_handle *trans,
>>> while (node) {
>>> ref = rb_entry(node, struct prelim_ref, rbnode);
>>> node = rb_next(&ref->rbnode);
>>> - WARN_ON(ref->count < 0);
>>> if (roots && ref->count && ref->root_id && ref->parent == 0) {
>>> if (sc && sc->root_objectid &&
>>> ref->root_id != sc->root_objectid) {
>>>
>
> Reviewed-by: Edmund Nadolski <enadol...@suse.com>
>
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