On Sat, 4 Jan 2025 at 12:26, Christian Brauner <brauner@xxxxxxxxxx> wrote:
>
> On Wed, Jan 01, 2025 at 07:05:10AM +1030, Qu Wenruo wrote:
> >
> >
> > 在 2024/12/30 19:59, Qu Wenruo 写道:
> > > Hi,
> > >
> > > Although I know it's triggered from btrfs, but the mnt_list handling is
> > > out of btrfs' control, so I'm here asking for some help.
>
> Thanks for the report.
>
> > >
> > > [BUG]
> > > With CONFIG_DEBUG_LIST and CONFIG_BUG_ON_DATA_CORRUPTION, and an
> > > upstream 6.13-rc kernel, which has commit 951a3f59d268 ("btrfs: fix
> > > mount failure due to remount races"), I can hit the following crash,
> > > with varied frequency (from 1/4 to hundreds runs no crash):
> >
> > There is also another WARNING triggered, without btrfs callback involved
> > at all:
> >
> > [ 192.688671] ------------[ cut here ]------------
> > [ 192.690016] WARNING: CPU: 3 PID: 59747 at fs/mount.h:150
>
> This would indicate that move_from_ns() was called on a mount that isn't
> attached to a mount namespace (anymore or never has).
Hi, I think the warning really means the mount just misses the
`MNT_ONRB` flag which actually should have been set. But for some
reason it is not.
And exactly the same applies to the reported crash.
```
1763 /* Gather the mounts to umount */
1764 for (p = mnt; p; p = next_mnt(p, mnt)) {
1765 p->mnt.mnt_flags |= MNT_UMOUNT;
1766 if (p->mnt.mnt_flags & MNT_ONRB)
1767 move_from_ns(p, &tmp_list);
1768 else
1769 list_move(&p->mnt_list, &tmp_list);
1770 }
```
Here the missing flag caused the crash in `list_move()` while
`move_from_ns()` should have been executed instead. All the evidence
supports this scenario. Due to the condition on line 1766 we got a
crash instead of the warning this time.
> Here's it's particularly peculiar because it looks like the warning is
> caused by calling move_from_ns() when moving a mount from an anonymous
> mount namespace in attach_recursive_mnt().
Indeed the crash happened with a detached mount in an anonymous mount namespace:
```
crash> mount.mnt_parent,mnt_ns 0xffff88810b9d0180
mnt_parent = 0xffff88810b9d0180, <<< Detached/root mount.
mnt_ns = 0xffff888103a12600,
crash> mnt_namespace.seq,mnt_ns_tree_node.__rb_parent_color 0xffff888103a12600
seq = 0x0, <<< Anonymous NS.
mnt_ns_tree_node.__rb_parent_color = 0xffff888103a12668, <<< Not
in the `mnt_ns_tree`.
```
It's also the condition which needs to be met in `do_move_mount()` to
not bail out before the warning in `attach_recursive_mnt()`:
```
3289 attached = mnt_has_parent(old);
--
3304 /* ... and either ours or the root of anon namespace */
3305 if (!(attached ? check_mnt(old) : is_anon_ns(ns)))
3306 goto out;
```
And the mount indeed is in the namespace mounts tree:
```
crash> mnt_namespace.root,mounts.rb_node ffff888103a12600
root = 0xffff88810b9d0180,
mounts.rb_node = 0xffff88810b9d0210
crash> mount.mnt_node 0xffff88810b9d0180
mnt_node = {
__rb_parent_color = 0x1,
rb_right = 0x0,
rb_left = 0x0
},
```
The `MNT_ONRB` flag should have been set so that the condition on line
1766 is true and we avoid the crash and `move_from_ns()` does not
complain with warning.
> Can you please try and reproduce this with
> commit 211364bef4301838b2e1 ("fs: kill MNT_ONRB")
This patch should indirectly address both errors but it does not
explain why the flag is sometimes missing.
--nX
> from the vfs-6.14.mount branch in
> https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git ?
>
> > attach_recursive_mnt+0xc58/0x1260
> > [ 192.692051] Modules linked in: nft_fib_inet nft_fib_ipv4 nft_fib_ipv6
> > nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct
> > nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4
> > nf_tables binfmt_misc btrfs xor raid6_pq zstd_compress iTCO_wdt
> > intel_pmc_bxt iTCO_vendor_support i2c_i801 i2c_smbus virtio_net
> > net_failover virtio_balloon lpc_ich failover joydev loop dm_multipath
> > nfnetlink vsock_loopback vmw_vsock_virtio_transport_common vsock zram
> > crct10dif_pclmul crc32_pclmul crc32c_intel polyval_clmulni
> > polyval_generic ghash_clmulni_intel sha512_ssse3 sha256_ssse3 sha1_ssse3
> > virtio_blk virtio_console bochs serio_raw scsi_dh_rdac scsi_dh_emc
> > scsi_dh_alua fuse qemu_fw_cfg
> > [ 192.707547] CPU: 3 UID: 0 PID: 59747 Comm: mount Kdump: loaded Not
> > tainted 6.13.0-rc4-custom+ #9
> > [ 192.709485] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
> > Arch Linux 1.16.3-1-1 04/01/2014
> > [ 192.711601] RIP: 0010:attach_recursive_mnt+0xc58/0x1260
> > [ 192.712725] Code: 85 c0 0f 85 79 ff ff ff 48 c7 c7 04 e7 00 8e 83 05
> > 9c 18 28 03 01 e8 97 1d c8 01 31 f6 48 89 ef e8 dd c1 fe ff e9 9c f5 ff
> > ff <0f> 0b e9 48 f8 ff ff 48 8b 44 24 10 48 8d 78 20 48 b8 00 00 00 00
> > [ 192.716521] RSP: 0018:ffff888105cafb68 EFLAGS: 00010246
> > [ 192.717621] RAX: 0000000000001020 RBX: ffff88811cc24030 RCX:
> > ffffffff8ca0e8e5
> > [ 192.719078] RDX: ffff888105cafbf0 RSI: ffff888118db0800 RDI:
> > ffff88811cc240f0
> > [ 192.720313] RBP: ffff88811cc24000 R08: ffff88810f21a840 R09:
> > ffffed1020b95f62
> > [ 192.721028] R10: 0000000000000003 R11: ffff88810a56e558 R12:
> > ffff88811cc24000
> > [ 192.721718] R13: dffffc0000000000 R14: ffff88810f21a840 R15:
> > ffff888105cafbf0
> > [ 192.722426] FS: 00007fdf69887800(0000) GS:ffff888236f80000(0000)
> > knlGS:0000000000000000
> > [ 192.723229] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [ 192.723849] CR2: 00007fdf697a9000 CR3: 000000010d925000 CR4:
> > 0000000000750ef0
> > [ 192.724549] PKRU: 55555554
> > [ 192.724860] Call Trace:
> > [ 192.725101] <TASK>
> > [ 192.725311] ? __warn.cold+0xb6/0x176
> > [ 192.725672] ? attach_recursive_mnt+0xc58/0x1260
> > [ 192.726149] ? report_bug+0x1f0/0x2a0
> > [ 192.726520] ? handle_bug+0x54/0x90
> > [ 192.726895] ? exc_invalid_op+0x17/0x40
> > [ 192.727259] ? asm_exc_invalid_op+0x1a/0x20
> > [ 192.727664] ? _raw_spin_lock+0x85/0xe0
> > [ 192.728053] ? attach_recursive_mnt+0xc58/0x1260
> > [ 192.728501] ? attach_recursive_mnt+0xb82/0x1260
> > [ 192.728954] ? _raw_spin_unlock+0xe/0x20
> > [ 192.729330] ? count_mounts+0x1e0/0x1e0
> > [ 192.729703] ? _raw_spin_lock+0x85/0xe0
> > [ 192.730082] ? _raw_write_lock_bh+0xe0/0xe0
> > [ 192.730493] do_move_mount+0x7a8/0x1a20
> > [ 192.730871] __do_sys_move_mount+0x7e2/0xcf0
> > [ 192.731288] ? syscall_exit_to_user_mode+0x10/0x200
> > [ 192.731762] ? do_syscall_64+0x8e/0x160
> > [ 192.732180] ? do_move_mount+0x1a20/0x1a20
> > [ 192.732587] do_syscall_64+0x82/0x160
> > [ 192.732950] ? syscall_exit_to_user_mode_prepare+0x15a/0x190
> > [ 192.733500] ? syscall_exit_to_user_mode+0x10/0x200
> > [ 192.733977] ? do_syscall_64+0x8e/0x160
> > [ 192.734374] ? from_kuid_munged+0x86/0x100
> > [ 192.734765] ? from_kuid+0xc0/0xc0
> > [ 192.735115] ? syscall_exit_to_user_mode_prepare+0x15a/0x190
> > [ 192.735644] ? syscall_exit_to_user_mode+0x10/0x200
> > [ 192.736124] ? do_syscall_64+0x8e/0x160
> > [ 192.736487] ? exc_page_fault+0x76/0xf0
> > [ 192.736861] entry_SYSCALL_64_after_hwframe+0x4b/0x53
> > [ 192.737352] RIP: 0033:0x7fdf69a5c3de
> > [ 192.737725] Code: 73 01 c3 48 8b 0d 32 3a 0f 00 f7 d8 64 89 01 48 83
> > c8 ff c3 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 49 89 ca b8 ad 01 00 00 0f
> > 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 02 3a 0f 00 f7 d8 64 89 01 48
> > [ 192.739455] RSP: 002b:00007ffd2b7c36d8 EFLAGS: 00000246 ORIG_RAX:
> > 00000000000001ad
> > [ 192.740176] RAX: ffffffffffffffda RBX: 0000557ac60e9a00 RCX:
> > 00007fdf69a5c3de
> > [ 192.740895] RDX: 00000000ffffff9c RSI: 00007fdf69bc9902 RDI:
> > 0000000000000004
> > [ 192.741578] RBP: 00007ffd2b7c3700 R08: 0000000000000004 R09:
> > 0000000000000001
> > [ 192.742247] R10: 0000557ac60e9e40 R11: 0000000000000246 R12:
> > 00007fdf69bd6b00
> > [ 192.742911] R13: 0000557ac60e9e40 R14: 0000557ac60ebbe0 R15:
> > 0000000000000066
> > [ 192.743573] </TASK>
> > [ 192.743803] ---[ end trace 0000000000000000 ]---
> >
> > Thanks,
> > Qu
> >
> > >
> > > [ 303.356328] BTRFS: device fsid 6fd8eb6f-1ea5-40aa-9857-05c64efe6d43
> > > devid 1 transid 9 /dev/mapper/test-scratch1 (253:2) scanned by mount
> > > (358060)
> > > [ 303.358614] BTRFS info (device dm-2): first mount of filesystem
> > > 6fd8eb6f-1ea5-40aa-9857-05c64efe6d43
> > > [ 303.359475] BTRFS info (device dm-2): using crc32c (crc32c-intel)
> > > checksum algorithm
> > > [ 303.360134] BTRFS info (device dm-2): using free-space-tree
> > > [ 313.264317] list_del corruption, ffff8fd48a7b2c90->prev is NULL
> > > [ 313.264966] ------------[ cut here ]------------
> > > [ 313.265402] kernel BUG at lib/list_debug.c:54!
> > > [ 313.265847] Oops: invalid opcode: 0000 [#1] PREEMPT SMP
> > > [ 313.266335] CPU: 4 UID: 0 PID: 370457 Comm: mount Kdump: loaded Not
> > > tainted 6.13.0-rc4-custom+ #8
> > > [ 313.267252] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
> > > Arch Linux 1.16.3-1-1 04/01/2014
> > > [ 313.268147] RIP: 0010:__list_del_entry_valid_or_report.cold+0x6d/0x6f
> > > [ 313.268777] Code: 05 77 a0 e8 4b 10 fd ff 0f 0b 48 89 fe 48 c7 c7 90
> > > 05 77 a0 e8 3a 10 fd ff 0f 0b 48 89 fe 48 c7 c7 60 05 77 a0 e8 29 10 fd
> > > ff <0f> 0b 4c 89 ea be 01 00 00 00 4c 89 44 24 48 48 c7 c7 20 7c 2b a1
> > > [ 313.270493] RSP: 0018:ffffa7620d2b3a38 EFLAGS: 00010246
> > > [ 313.270960] RAX: 0000000000000033 RBX: ffff8fd48a7b2c00 RCX:
> > > 0000000000000000
> > > [ 313.271565] RDX: 0000000000000000 RSI: ffff8fd5f7c21900 RDI:
> > > ffff8fd5f7c21900
> > > [ 313.272226] RBP: ffff8fd48a7b2c00 R08: 0000000000000000 R09:
> > > 0000000000000000
> > > [ 313.272895] R10: 74707572726f6320 R11: 6c65645f7473696c R12:
> > > ffffa7620d2b3a58
> > > [ 313.273521] R13: ffff8fd48a7b2c00 R14: 0000000000000000 R15:
> > > ffff8fd48a7b2c90
> > > [ 313.274138] FS: 00007f04740d4800(0000) GS:ffff8fd5f7c00000(0000)
> > > knlGS:0000000000000000
> > > [ 313.274864] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > [ 313.275392] CR2: 00007f0473ff6000 CR3: 000000011a8eb000 CR4:
> > > 0000000000750ef0
> > > [ 313.276084] PKRU: 55555554
> > > [ 313.276327] Call Trace:
> > > [ 313.276551] <TASK>
> > > [ 313.276752] ? __die_body.cold+0x19/0x28
> > > [ 313.277102] ? die+0x2e/0x50
> > > [ 313.277699] ? do_trap+0xc6/0x110
> > > [ 313.278033] ? do_error_trap+0x6a/0x90
> > > [ 313.278401] ? __list_del_entry_valid_or_report.cold+0x6d/0x6f
> > > [ 313.278941] ? exc_invalid_op+0x50/0x60
> > > [ 313.279308] ? __list_del_entry_valid_or_report.cold+0x6d/0x6f
> > > [ 313.279850] ? asm_exc_invalid_op+0x1a/0x20
> > > [ 313.280241] ? __list_del_entry_valid_or_report.cold+0x6d/0x6f
> > > [ 313.280777] ? __list_del_entry_valid_or_report.cold+0x6d/0x6f
> > > [ 313.281285] umount_tree+0xed/0x3c0
> > > [ 313.281589] put_mnt_ns+0x51/0x90
> > > [ 313.281886] mount_subtree+0x92/0x130
> > > [ 313.282205] btrfs_get_tree+0x343/0x6b0 [btrfs]
> > > [ 313.282785] vfs_get_tree+0x23/0xc0
> > > [ 313.283089] vfs_cmd_create+0x59/0xd0
> > > [ 313.283406] __do_sys_fsconfig+0x4eb/0x6b0
> > > [ 313.283764] do_syscall_64+0x82/0x160
> > > [ 313.284085] ? syscall_exit_to_user_mode_prepare+0x15a/0x190
> > > [ 313.284598] ? __fs_parse+0x68/0x1b0
> > > [ 313.284929] ? btrfs_parse_param+0x64/0x870 [btrfs]
> > > [ 313.285381] ? vfs_parse_fs_param_source+0x20/0x90
> > > [ 313.285825] ? __do_sys_fsconfig+0x1b8/0x6b0
> > > [ 313.286215] ? syscall_exit_to_user_mode_prepare+0x15a/0x190
> > > [ 313.286719] ? syscall_exit_to_user_mode+0x10/0x200
> > > [ 313.287151] ? do_syscall_64+0x8e/0x160
> > > [ 313.287498] ? vfs_fstatat+0x75/0xa0
> > > [ 313.287835] ? __do_sys_newfstatat+0x56/0x90
> > > [ 313.288240] ? syscall_exit_to_user_mode_prepare+0x15a/0x190
> > > [ 313.288749] ? syscall_exit_to_user_mode+0x10/0x200
> > > [ 313.289188] ? do_syscall_64+0x8e/0x160
> > > [ 313.289544] ? do_syscall_64+0x8e/0x160
> > > [ 313.289892] ? do_syscall_64+0x8e/0x160
> > > [ 313.290253] ? syscall_exit_to_user_mode+0x10/0x200
> > > [ 313.290692] ? do_syscall_64+0x8e/0x160
> > > [ 313.291034] ? exc_page_fault+0x7e/0x180
> > > [ 313.291380] entry_SYSCALL_64_after_hwframe+0x4b/0x53
> > > [ 313.291845] RIP: 0033:0x7f04742a919e
> > > [ 313.292182] Code: 73 01 c3 48 8b 0d 72 3c 0f 00 f7 d8 64 89 01 48 83
> > > c8 ff c3 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 49 89 ca b8 af 01 00 00 0f
> > > 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 42 3c 0f 00 f7 d8 64 89 01 48
> > > [ 313.293830] RSP: 002b:00007ffc3df08df8 EFLAGS: 00000246 ORIG_RAX:
> > > 00000000000001af
> > > [ 313.294529] RAX: ffffffffffffffda RBX: 000056407e37aa00 RCX:
> > > 00007f04742a919e
> > > [ 313.295201] RDX: 0000000000000000 RSI: 0000000000000006 RDI:
> > > 0000000000000003
> > > [ 313.295864] RBP: 00007ffc3df08f40 R08: 0000000000000000 R09:
> > > 0000000000000001
> > > [ 313.296602] R10: 0000000000000000 R11: 0000000000000246 R12:
> > > 00007f0474423b00
> > > [ 313.297416] R13: 0000000000000000 R14: 000056407e37cbe0 R15:
> > > 00007f0474418561
> > > [ 313.298242] </TASK>
> > > [ 313.298832] Modules linked in: nft_fib_inet nft_fib_ipv4 nft_fib_ipv6
> > > nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct
> > > nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4
> > > nf_tables binfmt_misc btrfs xor raid6_pq zstd_compress iTCO_wdt
> > > intel_pmc_bxt iTCO_vendor_support i2c_i801 i2c_smbus virtio_net joydev
> > > net_failover lpc_ich virtio_balloon failover loop dm_multipath nfnetlink
> > > vsock_loopback vmw_vsock_virtio_transport_common vsock zram
> > > crct10dif_pclmul crc32_pclmul crc32c_intel polyval_clmulni
> > > polyval_generic ghash_clmulni_intel virtio_console sha512_ssse3
> > > sha256_ssse3 bochs sha1_ssse3 virtio_blk serio_raw scsi_dh_rdac
> > > scsi_dh_emc scsi_dh_alua fuse qemu_fw_cfg
> > > [ 313.304504] Dumping ftrace buffer:
> > > [ 313.304876] (ftrace buffer empty)
> > >
> > > [EARLY ANALYZE]
> > >
> > > The offending line is the list_move() call inside unmount_tree().
> > >
> > > With crash core dump, the offending mnt_list is totally corrupted:
> > >
> > > crash> struct list_head ffff8fd48a7b2c90
> > > struct list_head {
> > > next = 0x1,
> > > prev = 0x0
> > > }
> > >
> > > umount_tree() should be protected by @mount_lock seqlock, and
> > > @namespace_sem rwsem.
> > >
> > > I also checked other mnt_list users:
> > >
> > > - commit_tree()
> > > - do_umount()
> > > - copy_tree()
> > >
> > > They all hold write @mount_lock at least.
> > >
> > > The only caller doesn't hold @mount_lock is iterate_mounts() but that's
> > > only called from audit, and I'm not sure if audit is even involved in
> > > this case.
>
> This is fine as audit creates a private copy of the mount tree it is
> interested in. The mount tree is not visible to other callers anymore.
>
> > >
> > > So I ran out of ideas why this mnt_list can even happen.
> > >
> > > Even if it's some btrfs' abuse, all mnt_list users are properly
> > > protected thus it should not lead to such list corruption.
> > >
> > > Any advice would be appreciated.
> > >
> > > Thanks,
> > > Qu
> > >
> >
>
