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Hello,
On Wed, 9 Oct 2019, Davide Caratti wrote:
> > Another possibility is the missing checks for
> > ip_vs_use_count_inc() result to cause underflow on ip_vs_use_count_dec().
>
> thanks for the advice, the unbalance is probably the cause of the splat
> I'm seeing. On a clean/unpatched kernel, I modified ip_vs_use_count() to
> do this:
>
> WARN_ON(!try_module_get(THIS_MODULE))
I think, the problem should be in step 2 below:
- step 1: try_stop_module -> try_release_module_ref -> atomic_sub_return
sets module refcnt to 0. After this point the process to remove module
can not be stopped and try_module_get() will fail in atomic_inc_not_zero.
- step 2: there is very small gap this step to occur: commands are
still registered and they should abort if try_module_get() fails.
This is what we see with WARN and oopses: ip_vs_use_count_inc can not
increment refcnt and we later fail in following ip_vs_use_count_dec.
Commands that add resources still do not need _inc + _dec but
those that increment module refcnt need the _inc check.
- step 3: ip_vs_unregister_nl_ioctl unregisters command handlers.
After this step commands are not running.
- step 4: release all module resources added up to step 2.
On module removal we do not expect to see stop_sync_thread()
stopping any running threads. The module can not be removed while
sync is running.
> using the reproducer below, I still see the splat in module_put(), but
> it's preceded by a failure in ip_vs_use_count_inc(), which accidentally is
> the same one I moved in my patch).
>
> IPVS: Registered protocols (TCP, UDP, SCTP, AH, ESP)
> IPVS: Connection hash table configured (size=4096, memory=64Kbytes)
> IPVS: ipvs loaded.
> IPVS: sync thread started: state = MASTER, mcast_ifn = veth_syncd, syncid =
> 0, id = 0
> IPVS: stopping master sync thread 4005 ...
> IPVS: sync thread started: state = MASTER, mcast_ifn = veth_syncd, syncid =
> 0, id = 0
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 4014 at net/netfilter/ipvs/ip_vs_ctl.c:235
> ip_vs_use_count_inc+0x19/0x20 [ip_vs]
> Modules linked in: ip_vs(-) nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 veth
> ip6table_filter ip6_tables iptable_filter binfmt_misc intel_rapl_msr
> intel_rapl_common crct10dif_pclmul crc32_pclmul ext4 mbcache jbd2
> ghash_clmulni_intel snd_hda_codec_generic ledtrig_audio snd_hda_intel
> snd_intel_nhlt snd_hda_codec snd_hda_core snd_hwdep snd_seq snd_seq_device
> snd_pcm aesni_intel crypto_simd cryptd glue_helper joydev pcspkr snd_timer
> virtio_balloon snd soundcore i2c_piix4 nfsd auth_rpcgss nfs_acl lockd grace
> sunrpc ip_tables xfs libcrc32c ata_generic pata_acpi virtio_net net_failover
> virtio_blk failover virtio_console qxl drm_kms_helper syscopyarea sysfillrect
> sysimgblt fb_sys_fops ata_piix ttm crc32c_intel serio_raw drm virtio_pci
> libata virtio_ring virtio floppy dm_mirror dm_region_hash dm_log dm_mod [last
> unloaded: nf_defrag_ipv6]
> CPU: 0 PID: 4014 Comm: ipvsadm Not tainted 5.4.0-rc1.upstream+ #741
> Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
> RIP: 0010:ip_vs_use_count_inc+0x19/0x20 [ip_vs]
> Code: e8 bc 5e dc f4 4c 8b 44 24 08 e9 db fd ff ff 66 90 0f 1f 44 00 00 48
> c7 c7 00 02 42 c1 e8 5f 3c 9e f4 84 c0 74 04 0f b6 c0 c3 <0f> 0b 0f b6 c0 c3
> 90 0f 1f 44 00 00 55 48 89 e5 41 57 49 89 f7 41
> RSP: 0018:ffff88804ba5f2c8 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: ffff88804f533ca8 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: 1ffff1100974be3f RDI: ffffffffc1420200
> RBP: ffff88804ba5f500 R08: fffffbfff71129d1 R09: fffffbfff71129d1
> R10: 0000000000000001 R11: fffffbfff71129d0 R12: ffff88804f533300
> R13: 0000000000000000 R14: 0000000000000001 R15: ffff888079442d00
> FS: 00007fd42ff9c740(0000) GS:ffff888053800000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000fc91d8 CR3: 000000004fe2c002 CR4: 00000000001606f0
> Call Trace:
> start_sync_thread+0x1c17/0x23a0 [ip_vs]
> ip_vs_genl_new_daemon+0x3b0/0x550 [ip_vs]
> ip_vs_genl_set_daemon+0x295/0x360 [ip_vs]
> genl_rcv_msg+0x588/0x11e0
> netlink_rcv_skb+0x121/0x350
> genl_rcv+0x24/0x40
> netlink_unicast+0x416/0x5d0
> netlink_sendmsg+0x67f/0xb50
> sock_sendmsg+0xe2/0x110
> ___sys_sendmsg+0x640/0x940
> __sys_sendmsg+0xd2/0x170
> do_syscall_64+0xa5/0x4e0
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x7fd42f48f930
> Code: c3 48 8b 05 42 75 2c 00 f7 db 64 89 18 48 83 cb ff eb dd 0f 1f 80 00
> 00 00 00 83 3d 6d d6 2c 00 00 75 10 b8 2e 00 00 00 0f 05 <48> 3d 01 f0 ff ff
> 73 31 c3 48 83 ec 08 e8 ae cc 00 00 48 89 04 24
> RSP: 002b:00007ffcf69ecaa8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 0000000000fc2100 RCX: 00007fd42f48f930
> RDX: 0000000000000000 RSI: 00007ffcf69ecb50 RDI: 0000000000000003
> RBP: 0000000000fc2010 R08: 0000000000000001 R09: 0000000000fc2150
> R10: 00007fd42f7577b8 R11: 0000000000000246 R12: 0000000000fc3160
> R13: 00007ffcf69ecb50 R14: 0000000000000000 R15: 0000000000000000
> irq event stamp: 3288
> hardirqs last enabled at (3287): [<ffffffffb5bb276f>]
> __local_bh_enable_ip+0xef/0x1b0
> hardirqs last disabled at (3288): [<ffffffffb5a0556a>]
> trace_hardirqs_off_thunk+0x1a/0x20
> softirqs last enabled at (3286): [<ffffffffc13f3365>]
> start_sync_thread+0x1c05/0x23a0 [ip_vs]
> softirqs last disabled at (3284): [<ffffffffc13f32e1>]
> start_sync_thread+0x1b81/0x23a0 [ip_vs]
> ---[ end trace 7b4e216440e510e6 ]---
> IPVS: stopping master sync thread 4016 ...
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 4013 at kernel/module.c:1146
> module_put.part.44+0x15b/0x290
> Modules linked in: ip_vs(-) nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 veth
> ip6table_filter ip6_tables iptable_filter binfmt_misc intel_rapl_msr
> intel_rapl_common crct10dif_pclmul crc32_pclmul ext4 mbcache jbd2
> ghash_clmulni_intel snd_hda_codec_generic ledtrig_audio snd_hda_intel
> snd_intel_nhlt snd_hda_codec snd_hda_core snd_hwdep snd_seq snd_seq_device
> snd_pcm aesni_intel crypto_simd cryptd glue_helper joydev pcspkr snd_timer
> virtio_balloon snd soundcore i2c_piix4 nfsd auth_rpcgss nfs_acl lockd grace
> sunrpc ip_tables xfs libcrc32c ata_generic pata_acpi virtio_net net_failover
> virtio_blk failover virtio_console qxl drm_kms_helper syscopyarea sysfillrect
> sysimgblt fb_sys_fops ata_piix ttm crc32c_intel serio_raw drm virtio_pci
> libata virtio_ring virtio floppy dm_mirror dm_region_hash dm_log dm_mod [last
> unloaded: nf_defrag_ipv6]
> CPU: 0 PID: 4013 Comm: modprobe Tainted: G W
> 5.4.0-rc1.upstream+ #741
> Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
> RIP: 0010:module_put.part.44+0x15b/0x290
> Code: 04 25 28 00 00 00 0f 85 18 01 00 00 48 83 c4 68 5b 5d 41 5c 41 5d 41
> 5e 41 5f c3 89 44 24 28 83 e8 01 89 c5 0f 89 57 ff ff ff <0f> 0b e9 78 ff ff
> ff 65 8b 1d 67 83 26 4a 89 db be 08 00 00 00 48
> RSP: 0018:ffff888050607c78 EFLAGS: 00010297
> RAX: 0000000000000003 RBX: ffffffffc1420590 RCX: ffffffffb5db0ef9
> RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffffffffc1420590
> RBP: 00000000ffffffff R08: fffffbfff82840b3 R09: fffffbfff82840b3
> R10: 0000000000000001 R11: fffffbfff82840b2 R12: 1ffff1100a0c0f90
> R13: ffffffffc1420200 R14: ffff88804f533300 R15: ffff88804f533ca0
> FS: 00007f8ea9720740(0000) GS:ffff888053800000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f3245abe000 CR3: 000000004c28a006 CR4: 00000000001606f0
> Call Trace:
> stop_sync_thread+0x3a3/0x7c0 [ip_vs]
> ip_vs_sync_net_cleanup+0x13/0x50 [ip_vs]
> ops_exit_list.isra.5+0x94/0x140
> unregister_pernet_operations+0x29d/0x460
> unregister_pernet_device+0x26/0x60
> ip_vs_cleanup+0x11/0x38 [ip_vs]
> __x64_sys_delete_module+0x2d5/0x400
> do_syscall_64+0xa5/0x4e0
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x7f8ea8bf0db7
> Code: 73 01 c3 48 8b 0d b9 80 2c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f
> 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 b0 00 00 00 0f 05 <48> 3d 01 f0 ff ff
> 73 01 c3 48 8b 0d 89 80 2c 00 f7 d8 64 89 01 48
> RSP: 002b:00007ffcd38d2fe8 EFLAGS: 00000206 ORIG_RAX: 00000000000000b0
> RAX: ffffffffffffffda RBX: 0000000002436240 RCX: 00007f8ea8bf0db7
> RDX: 0000000000000000 RSI: 0000000000000800 RDI: 00000000024362a8
> RBP: 0000000000000000 R08: 00007f8ea8eba060 R09: 00007f8ea8c658a0
> R10: 00007ffcd38d2a60 R11: 0000000000000206 R12: 0000000000000000
> R13: 0000000000000001 R14: 00000000024362a8 R15: 0000000000000000
> irq event stamp: 4538
> hardirqs last enabled at (4537): [<ffffffffb6193dde>]
> quarantine_put+0x9e/0x170
> hardirqs last disabled at (4538): [<ffffffffb5a0556a>]
> trace_hardirqs_off_thunk+0x1a/0x20
> softirqs last enabled at (4522): [<ffffffffb6f8ebe9>]
> sk_common_release+0x169/0x2d0
> softirqs last disabled at (4520): [<ffffffffb6f8eb3e>]
> sk_common_release+0xbe/0x2d0
> ---[ end trace 7b4e216440e510e7 ]---
> IPVS: ipvs unloaded.
>
> so, this is try_module_get() in ip_vs_start_sync_thread() failing to refcount
> ip_vs.
Yes, refcnt is not increased.
> When the module is unloaded and stop_sync_thread() is called, the refcounts
> are
> unbalanced and then we see the splat when the last module_put() is called.
module_put on refcnt 0
> > Are there any steps to reproduce?
>
> yes, a script that does the following:
>
> while true; do
> if modprobe -r ip_vs; then
> sleep 0.5
> fi
> done >/dev/null 2>&1 &
>
> while true; do
> ipvsadm --start-daemon master --mcast-interface veth_syncd
> done >/dev/null 2>&1 &
>
> while true; do
> ipvsadm --stop-daemon master
> done >/dev/null 2>&1
>
>
> I'm about to send a v2 patch where I test the return value of each call to
> ip_vs_use_count_inc(), and jump to the error path of caller functions
> (returning -EAGAIN) on failure of try_module_get(). For
> ip_vs_start_sync_thread(), the resulting code is very similar to what I
> did in the first post, with the only addition of an additional 'goto
> out_unlock;' in case the attempt to refcount the module failed.
Yes, every place that increments refcnt would
need early ip_vs_use_count_inc() call with result check. Then check in
do_ip_vs_set_ctl() would not be needed, any resources we modify would be
released after the ip_vs_unregister_nl_ioctl call.
For the other files, check is needed in register_ip_vs_pe() and
register_ip_vs_scheduler(), register_ip_vs_app() should
_inc+check and _dec on failure.
Regards
--
Julian Anastasov <ja@xxxxxx>
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