[syzbot] [mm?] WARNING in unlink_anon_vmas (2)

[syzbot] [mm?] WARNING in unlink_anon_vmas (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    b775e489bec7 Add linux-next specific files for 20260114
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15dbc444580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2dcf53f0a51185
dashboard link: https://syzkaller.appspot.com/bug?extid=c27fa543e10a45d4e149
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17070522580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1683f99a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/5e077e7eafdc/disk-b775e489.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ea69aef6ee56/vmlinux-b775e489.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b8b6986280d1/bzImage-b775e489.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c27fa543e10a45d4e149@syzkaller.appspotmail.com

R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000002
R13: 00007f16655e5fa0 R14: 00007f16655e5fa0 R15: 0000000000000002
 </TASK>
------------[ cut here ]------------
WARNING: mm/rmap.c:480 at unlink_anon_vmas+0x701/0x730 mm/rmap.c:480, CPU#0: syz.0.20/5987
Modules linked in:
CPU: 0 UID: 0 PID: 5987 Comm: syz.0.20 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:unlink_anon_vmas+0x701/0x730 mm/rmap.c:480
Code: ac ff 48 83 c4 40 5b 41 5c 41 5d 41 5e 41 5f 5d e9 84 df 56 09 cc e8 8e ed ac ff 90 0f 0b 90 e9 e2 f9 ff ff e8 80 ed ac ff 90 <0f> 0b 90 eb d3 48 c7 c1 10 ab c4 8f 80 e1 07 80 c1 03 38 c1 0f 8c
RSP: 0018:ffffc900033676c0 EFLAGS: 00010293
RAX: ffffffff821460b0 RBX: dffffc0000000000 RCX: ffff88802a773c80
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: 0000000000000001 R08: ffffffff8fc47af7 R09: 1ffffffff1f88f5e
R10: dffffc0000000000 R11: fffffbfff1f88f5f R12: 1ffff110062fbaa8
R13: ffff888027aad900 R14: ffff8880317dd510 R15: ffff8880317dd530
FS:  0000555592787500(0000) GS:ffff8881259ad000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f166526615a CR3: 000000002f0cc000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 anon_vma_fork+0x4b9/0x500 mm/rmap.c:438
 dup_mmap+0x954/0x1b80 mm/mmap.c:1790
 dup_mm kernel/fork.c:1529 [inline]
 copy_mm+0x13c/0x4b0 kernel/fork.c:1581
 copy_process+0x1812/0x3ba0 kernel/fork.c:2218
 kernel_clone+0x21e/0x820 kernel/fork.c:2648
 __do_sys_clone3 kernel/fork.c:2950 [inline]
 __se_sys_clone3+0x256/0x2d0 kernel/fork.c:2929
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f166538f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe55f4df08 EFLAGS: 00000246 ORIG_RAX: 00000000000001b3
RAX: ffffffffffffffda RBX: 0000000000000058 RCX: 00007f166538f749
RDX: 00007ffe55f4df20 RSI: 0000000000000058 RDI: 00007ffe55f4df20
RBP: 00007ffe55f4e090 R08: 0000000000000000 R09: 0000000000000058
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000002
R13: 00007f16655e5fa0 R14: 00007f16655e5fa0 R15: 0000000000000002
 </TASK>


---
This report is generated by a bot. It may contain errors.
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If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
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(See the list of subsystem names on the web dashboard)

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#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

Re: [syzbot] [mm?] WARNING in unlink_anon_vmas (2)

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

SYZFAIL: failed to recv rpc

SYZFAIL: failed to recv rpc
fd=3 want=4 recv=0 n=0 (errno 9: Bad file descriptor)


Warning: Permanently added '10.128.1.53' (ED25519) to the list of known hosts.
2026/01/18 09:20:01 parsed 1 programs
[   77.901035][ T5828] cgroup: Unknown subsys name 'net'
[   78.037193][ T5828] cgroup: Unknown subsys name 'cpuset'
[   78.046859][ T5828] cgroup: Unknown subsys name 'rlimit'
Setting up swapspace version 1, size = 127995904 bytes
[   79.512011][ T5828] Adding 124996k swap on ./swap-file.  Priority:0 extents:1 across:124996k 
[   82.341391][ T5835] soft_limit_in_bytes is deprecated and will be removed. Please report your usecase to linux-mm@kvack.org if you depend on this functionality.
[   83.758436][ T1015] wlan0: Created IBSS using preconfigured BSSID 50:50:50:50:50:50
[   83.774306][ T1015] wlan0: Creating new IBSS network, BSSID 50:50:50:50:50:50
[   83.821559][ T1015] wlan1: Created IBSS using preconfigured BSSID 50:50:50:50:50:50
[   83.831495][ T1015] wlan1: Creating new IBSS network, BSSID 50:50:50:50:50:50
[   85.270179][ T5897] chnl_net:caif_netlink_parms(): no params data found
[   85.377098][ T5897] bridge0: port 1(bridge_slave_0) entered blocking state
[   85.385837][ T5897] bridge0: port 1(bridge_slave_0) entered disabled state
[   85.393932][ T5897] bridge_slave_0: entered allmulticast mode
[   85.406735][ T5897] bridge_slave_0: entered promiscuous mode
[   85.417915][ T5897] bridge0: port 2(bridge_slave_1) entered blocking state
[   85.425327][ T5897] bridge0: port 2(bridge_slave_1) entered disabled state
[   85.433157][ T5897] bridge_slave_1: entered allmulticast mode
[   85.440912][ T5897] bridge_slave_1: entered promiscuous mode
[   85.474547][ T5897] bond0: (slave bond_slave_0): Enslaving as an active interface with an up link
[   85.487901][ T5897] bond0: (slave bond_slave_1): Enslaving as an active interface with an up link
[   85.518305][ T5897] team0: Port device team_slave_0 added
[   85.527422][ T5897] team0: Port device team_slave_1 added
[   85.555868][ T5897] batman_adv: batadv0: Adding interface: batadv_slave_0
[   85.562935][ T5897] batman_adv: batadv0: The MTU of interface batadv_slave_0 is too small (1500) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1532 would solve the problem.
[   85.590621][ T5897] batman_adv: batadv0: Not using interface batadv_slave_0 (retrying later): interface not active
[   85.605927][ T5897] batman_adv: batadv0: Adding interface: batadv_slave_1
[   85.613503][ T5897] batman_adv: batadv0: The MTU of interface batadv_slave_1 is too small (1500) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1532 would solve the problem.
[   85.639963][ T5897] batman_adv: batadv0: Not using interface batadv_slave_1 (retrying later): interface not active
[   85.684487][ T5897] hsr_slave_0: entered promiscuous mode
[   85.691316][ T5897] hsr_slave_1: entered promiscuous mode
[   85.859484][ T5897] netdevsim netdevsim0 netdevsim0: renamed from eth0
[   85.874651][ T5897] netdevsim netdevsim0 netdevsim1: renamed from eth1
[   85.886048][ T5897] netdevsim netdevsim0 netdevsim2: renamed from eth2
[   85.897250][ T5897] netdevsim netdevsim0 netdevsim3: renamed from eth3
[   85.977012][ T5897] 8021q: adding VLAN 0 to HW filter on device bond0
[   85.999505][ T5897] 8021q: adding VLAN 0 to HW filter on device team0
[   86.015481][   T48] bridge0: port 1(bridge_slave_0) entered blocking state
[   86.022966][   T48] bridge0: port 1(bridge_slave_0) entered forwarding state
[   86.043961][  T138] bridge0: port 2(bridge_slave_1) entered blocking state
[   86.051117][  T138] bridge0: port 2(bridge_slave_1) entered forwarding state
[   86.228809][ T5897] 8021q: adding VLAN 0 to HW filter on device batadv0
[   86.286274][ T5897] veth0_vlan: entered promiscuous mode
[   86.299783][ T5897] veth1_vlan: entered promiscuous mode
[   86.329644][ T5897] veth0_macvtap: entered promiscuous mode
[   86.343054][ T5897] veth1_macvtap: entered promiscuous mode
[   86.363147][ T5897] batman_adv: batadv0: Interface activated: batadv_slave_0
[   86.380112][ T5897] batman_adv: batadv0: Interface activated: batadv_slave_1
[   86.399133][   T48] netdevsim netdevsim0 netdevsim0: set [1, 0] type 2 family 0 port 6081 - 0
[   86.410010][   T48] netdevsim netdevsim0 netdevsim1: set [1, 0] type 2 family 0 port 6081 - 0
[   86.421091][   T48] netdevsim netdevsim0 netdevsim2: set [1, 0] type 2 family 0 port 6081 - 0
[   86.432173][   T48] netdevsim netdevsim0 netdevsim3: set [1, 0] type 2 family 0 port 6081 - 0
[   86.598062][ T5150] Bluetooth: hci0: unexpected cc 0x0c03 length: 249 > 1
[   86.607913][ T5150] Bluetooth: hci0: unexpected cc 0x1003 length: 249 > 9
[   86.609158][  T138] netdevsim netdevsim0 netdevsim3 (unregistering): unset [1, 0] type 2 family 0 port 6081 - 0
[   86.623754][ T5150] Bluetooth: hci0: unexpected cc 0x1001 length: 249 > 9
[   86.636311][ T5150] Bluetooth: hci0: unexpected cc 0x0c23 length: 249 > 4
[   86.645064][ T5150] Bluetooth: hci0: unexpected cc 0x0c38 length: 249 > 2
[   86.691225][  T138] netdevsim netdevsim0 netdevsim2 (unregistering): unset [1, 0] type 2 family 0 port 6081 - 0
[   86.743066][  T138] netdevsim netdevsim0 netdevsim1 (unregistering): unset [1, 0] type 2 family 0 port 6081 - 0
[   86.808471][  T138] netdevsim netdevsim0 netdevsim0 (unregistering): unset [1, 0] type 2 family 0 port 6081 - 0
2026/01/18 09:20:13 executed programs: 0
[   87.897627][ T5150] Bluetooth: hci0: unexpected cc 0x0c03 length: 249 > 1
[   87.907311][ T5150] Bluetooth: hci0: unexpected cc 0x1003 length: 249 > 9
[   87.917067][ T5150] Bluetooth: hci0: unexpected cc 0x1001 length: 249 > 9
[   87.926516][ T5150] Bluetooth: hci0: unexpected cc 0x0c23 length: 249 > 4
[   87.934931][ T5150] Bluetooth: hci0: unexpected cc 0x0c38 length: 249 > 2
[   88.101828][ T5940] chnl_net:caif_netlink_parms(): no params data found
[   88.175963][ T5940] bridge0: port 1(bridge_slave_0) entered blocking state
[   88.183508][ T5940] bridge0: port 1(bridge_slave_0) entered disabled state
[   88.190988][ T5940] bridge_slave_0: entered allmulticast mode
[   88.198822][ T5940] bridge_slave_0: entered promiscuous mode
[   88.214722][ T5940] bridge0: port 2(bridge_slave_1) entered blocking state
[   88.222402][ T5940] bridge0: port 2(bridge_slave_1) entered disabled state
[   88.229826][ T5940] bridge_slave_1: entered allmulticast mode
[   88.237116][ T5940] bridge_slave_1: entered promiscuous mode
[   88.272871][ T5940] bond0: (slave bond_slave_0): Enslaving as an active interface with an up link
[   88.285334][ T5940] bond0: (slave bond_slave_1): Enslaving as an active interface with an up link
[   88.320146][ T5940] team0: Port device team_slave_0 added
[   88.329176][ T5940] team0: Port device team_slave_1 added
[   88.356327][ T5940] batman_adv: batadv0: Adding interface: batadv_slave_0
[   88.363729][ T5940] batman_adv: batadv0: The MTU of interface batadv_slave_0 is too small (1500) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1532 would solve the problem.
[   88.390930][ T5940] batman_adv: batadv0: Not using interface batadv_slave_0 (retrying later): interface not active
[   88.404526][ T5940] batman_adv: batadv0: Adding interface: batadv_slave_1
[   88.411643][ T5940] batman_adv: batadv0: The MTU of interface batadv_slave_1 is too small (1500) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1532 would solve the problem.
[   88.440029][ T5940] batman_adv: batadv0: Not using interface batadv_slave_1 (retrying later): interface not active
[   88.488754][ T5940] hsr_slave_0: entered promiscuous mode
[   88.495800][ T5940] hsr_slave_1: entered promiscuous mode
[   88.502287][ T5940] debugfs: 'hsr0' already exists in 'hsr'
[   88.509149][ T5940] Cannot create hsr debugfs directory
[   89.269277][  T138] bridge_slave_1: left allmulticast mode
[   89.276040][  T138] bridge_slave_1: left promiscuous mode
[   89.282780][  T138] bridge0: port 2(bridge_slave_1) entered disabled state
[   89.296292][  T138] bridge_slave_0: left allmulticast mode
[   89.301959][  T138] bridge_slave_0: left promiscuous mode
[   89.308602][  T138] bridge0: port 1(bridge_slave_0) entered disabled state
[   89.628117][  T138] bond0 (unregistering): (slave bond_slave_0): Releasing backup interface
[   89.640101][  T138] bond0 (unregistering): (slave bond_slave_1): Releasing backup interface
[   89.656329][  T138] bond0 (unregistering): Released all slaves
[   89.792085][  T138] hsr_slave_0: left promiscuous mode
[   89.798862][  T138] hsr_slave_1: left promiscuous mode
[   89.805585][  T138] batman_adv: batadv0: Interface deactivated: batadv_slave_0
[   89.823607][  T138] batman_adv: batadv0: Removing interface: batadv_slave_0
[   89.845653][  T138] batman_adv: batadv0: Interface deactivated: batadv_slave_1
[   89.857800][  T138] batman_adv: batadv0: Removing interface: batadv_slave_1
[   89.886296][  T138] veth1_macvtap: left promiscuous mode
[   89.894314][  T138] veth0_macvtap: left promiscuous mode
[   89.900282][  T138] veth1_vlan: left promiscuous mode
[   89.906625][  T138] veth0_vlan: left promiscuous mode
[   89.974848][ T5150] Bluetooth: hci0: command tx timeout
[   90.443879][  T138] team0 (unregistering): Port device team_slave_1 removed
[   90.484332][  T138] team0 (unregistering): Port device team_slave_0 removed
[   91.120268][ T5940] netdevsim netdevsim0 netdevsim0: renamed from eth0
[   91.141856][ T5940] netdevsim netdevsim0 netdevsim1: renamed from eth1
[   91.156300][ T5940] netdevsim netdevsim0 netdevsim2: renamed from eth2
[   91.180803][ T5940] netdevsim netdevsim0 netdevsim3: renamed from eth3
[   91.492926][ T5940] 8021q: adding VLAN 0 to HW filter on device bond0
[   91.548808][ T5940] 8021q: adding VLAN 0 to HW filter on device team0
[   91.570918][ T1015] bridge0: port 1(bridge_slave_0) entered blocking state
[   91.578359][ T1015] bridge0: port 1(bridge_slave_0) entered forwarding state
[   91.638837][ T1015] bridge0: port 2(bridge_slave_1) entered blocking state
[   91.646007][ T1015] bridge0: port 2(bridge_slave_1) entered forwarding state
[   91.688028][ T5940] hsr0: Slave B (hsr_slave_1) is not up; please bring it up to get a fully working HSR network
[   91.861733][ T5940] 8021q: adding VLAN 0 to HW filter on device batadv0
[   91.913142][ T5940] veth0_vlan: entered promiscuous mode
[   91.927519][ T5940] veth1_vlan: entered promiscuous mode
[   91.959185][ T5940] veth0_macvtap: entered promiscuous mode
[   91.969886][ T5940] veth1_macvtap: entered promiscuous mode
[   91.988597][ T5940] batman_adv: batadv0: Interface activated: batadv_slave_0
[   92.003588][ T5940] batman_adv: batadv0: Interface activated: batadv_slave_1
[   92.018996][  T138] netdevsim netdevsim0 netdevsim0: set [1, 0] type 2 family 0 port 6081 - 0
[   92.029337][  T138] netdevsim netdevsim0 netdevsim1: set [1, 0] type 2 family 0 port 6081 - 0
[   92.041299][  T138] netdevsim netdevsim0 netdevsim2: set [1, 0] type 2 family 0 port 6081 - 0
[   92.052158][  T138] netdevsim netdevsim0 netdevsim3: set [1, 0] type 2 family 0 port 6081 - 0
[   92.054178][ T5150] Bluetooth: hci0: command tx timeout
[   92.126119][  T138] wlan0: Created IBSS using preconfigured BSSID 50:50:50:50:50:50
[   92.140328][  T138] wlan0: Creating new IBSS network, BSSID 50:50:50:50:50:50
[   92.170290][ T1015] wlan1: Created IBSS using preconfigured BSSID 50:50:50:50:50:50
[   92.178614][ T1015] wlan1: Creating new IBSS network, BSSID 50:50:50:50:50:50
SYZFAIL: failed to recv rpc
fd=3 want=4 recv=0 n=0 (errno 9: Bad file descriptor)
[   92.539270][   T49] cfg80211: failed to load regulatory.db


syzkaller build log:
go env (err=<nil>)
AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE='auto'
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/syzkaller/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/syzkaller/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build1432137956=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/syzkaller/jobs-2/linux/gopath/src/github.com/google/syzkaller/go.mod'
GOMODCACHE='/syzkaller/jobs-2/linux/gopath/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/syzkaller/jobs-2/linux/gopath'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/syzkaller/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.24.4'
GOWORK=''
PKG_CONFIG='pkg-config'

git status (err=<nil>)
HEAD detached at d6526ea3e
nothing to commit, working tree clean


tput: No value for $TERM and no -T specified
tput: No value for $TERM and no -T specified
Makefile:31: run command via tools/syz-env for best compatibility, see:
Makefile:32: https://github.com/google/syzkaller/blob/master/docs/contributing.md#using-syz-env
go list -f '{{.Stale}}' -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=d6526ea3e6ad9081c902859bbb80f9f840377cb4 -X github.com/google/syzkaller/prog.gitRevisionDate=20251126-113115"  ./sys/syz-sysgen | grep -q false || go install -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=d6526ea3e6ad9081c902859bbb80f9f840377cb4 -X github.com/google/syzkaller/prog.gitRevisionDate=20251126-113115"  ./sys/syz-sysgen
make .descriptions
tput: No value for $TERM and no -T specified
tput: No value for $TERM and no -T specified
Makefile:31: run command via tools/syz-env for best compatibility, see:
Makefile:32: https://github.com/google/syzkaller/blob/master/docs/contributing.md#using-syz-env
bin/syz-sysgen
touch .descriptions
GOOS=linux GOARCH=amd64 go build -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=d6526ea3e6ad9081c902859bbb80f9f840377cb4 -X github.com/google/syzkaller/prog.gitRevisionDate=20251126-113115"  -o ./bin/linux_amd64/syz-execprog github.com/google/syzkaller/tools/syz-execprog
mkdir -p ./bin/linux_amd64
g++ -o ./bin/linux_amd64/syz-executor executor/executor.cc \
	-m64 -O2 -pthread -Wall -Werror -Wparentheses -Wunused-const-variable -Wframe-larger-than=16384 -Wno-stringop-overflow -Wno-array-bounds -Wno-format-overflow -Wno-unused-but-set-variable -Wno-unused-command-line-argument -static-pie -std=c++17 -I. -Iexecutor/_include   -DGOOS_linux=1 -DGOARCH_amd64=1 \
	-DHOSTGOOS_linux=1 -DGIT_REVISION=\"d6526ea3e6ad9081c902859bbb80f9f840377cb4\"
/usr/bin/ld: /tmp/ccDM8VfB.o: in function `Connection::Connect(char const*, char const*)':
executor.cc:(.text._ZN10Connection7ConnectEPKcS1_[_ZN10Connection7ConnectEPKcS1_]+0x104): warning: Using 'gethostbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
./tools/check-syzos.sh 2>/dev/null



Tested on:

commit:         46fe65a2 Add linux-next specific files for 20260116
git tree:       linux-next
kernel config:  https://syzkaller.appspot.com/x/.config?x=9c0b39f55c418575
dashboard link: https://syzkaller.appspot.com/bug?extid=c27fa543e10a45d4e149
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=10fb33fc580000

Re: [syzbot] [mm?] WARNING in unlink_anon_vmas (2)

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+c27fa543e10a45d4e149@syzkaller.appspotmail.com
Tested-by: syzbot+c27fa543e10a45d4e149@syzkaller.appspotmail.com

Tested on:

commit:         46fe65a2 Add linux-next specific files for 20260116
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=12646b9a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9c0b39f55c418575
dashboard link: https://syzkaller.appspot.com/bug?extid=c27fa543e10a45d4e149
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=102c8b9a580000

Note: testing is done by a robot and is best-effort only.

Re: [syzbot] [mm?] WARNING in unlink_anon_vmas (2)

[Lorenzo Stoakes]

On Sat, Jan 17, 2026 at 11:30:24PM -0800, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    b775e489bec7 Add linux-next specific files for 20260114
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=15dbc444580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=2dcf53f0a51185
> dashboard link: https://syzkaller.appspot.com/bug?extid=c27fa543e10a45d4e149
> compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17070522580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1683f99a580000

Thanks, of course being a fault injection thing it's hard to repro :))

>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/5e077e7eafdc/disk-b775e489.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/ea69aef6ee56/vmlinux-b775e489.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/b8b6986280d1/bzImage-b775e489.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+c27fa543e10a45d4e149@syzkaller.appspotmail.com
>
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000002
> R13: 00007f16655e5fa0 R14: 00007f16655e5fa0 R15: 0000000000000002
>  </TASK>
> ------------[ cut here ]------------
> WARNING: mm/rmap.c:480 at unlink_anon_vmas+0x701/0x730 mm/rmap.c:480, CPU#0: syz.0.20/5987
> Modules linked in:
> CPU: 0 UID: 0 PID: 5987 Comm: syz.0.20 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
> RIP: 0010:unlink_anon_vmas+0x701/0x730 mm/rmap.c:480
> Code: ac ff 48 83 c4 40 5b 41 5c 41 5d 41 5e 41 5f 5d e9 84 df 56 09 cc e8 8e ed ac ff 90 0f 0b 90 e9 e2 f9 ff ff e8 80 ed ac ff 90 <0f> 0b 90 eb d3 48 c7 c1 10 ab c4 8f 80 e1 07 80 c1 03 38 c1 0f 8c
> RSP: 0018:ffffc900033676c0 EFLAGS: 00010293
> RAX: ffffffff821460b0 RBX: dffffc0000000000 RCX: ffff88802a773c80
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
> RBP: 0000000000000001 R08: ffffffff8fc47af7 R09: 1ffffffff1f88f5e
> R10: dffffc0000000000 R11: fffffbfff1f88f5f R12: 1ffff110062fbaa8
> R13: ffff888027aad900 R14: ffff8880317dd510 R15: ffff8880317dd530
> FS:  0000555592787500(0000) GS:ffff8881259ad000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f166526615a CR3: 000000002f0cc000 CR4: 00000000003526f0
> Call Trace:
>  <TASK>

Yup this is a nasty additional and impossible-to-hit-in-practice case the
series didn't account for, this time in anon_vma_fork().

Very annoyingly, it violates assumptions made because we try to free up a
partially set up anon_vma.

I'll rework my series + respin to account for this.

Cheers, Lorenzo

>  anon_vma_fork+0x4b9/0x500 mm/rmap.c:438
>  dup_mmap+0x954/0x1b80 mm/mmap.c:1790
>  dup_mm kernel/fork.c:1529 [inline]
>  copy_mm+0x13c/0x4b0 kernel/fork.c:1581
>  copy_process+0x1812/0x3ba0 kernel/fork.c:2218
>  kernel_clone+0x21e/0x820 kernel/fork.c:2648
>  __do_sys_clone3 kernel/fork.c:2950 [inline]
>  __se_sys_clone3+0x256/0x2d0 kernel/fork.c:2929
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f166538f749
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffe55f4df08 EFLAGS: 00000246 ORIG_RAX: 00000000000001b3
> RAX: ffffffffffffffda RBX: 0000000000000058 RCX: 00007f166538f749
> RDX: 00007ffe55f4df20 RSI: 0000000000000058 RDI: 00007ffe55f4df20
> RBP: 00007ffe55f4e090 R08: 0000000000000000 R09: 0000000000000058
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000002
> R13: 00007f16655e5fa0 R14: 00007f16655e5fa0 R15: 0000000000000002
>  </TASK>
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
>
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.
>
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
>
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
>
> If you want to undo deduplication, reply with:
> #syz undup