[syzbot] [mm?] WARNING in move_page_tables

[syzbot] [mm?] WARNING in move_page_tables

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    53e760d89498 Merge tag 'nfsd-6.17-1' of git://git.kernel.o..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=165fe9a2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f9319a42cfb3bf57
dashboard link: https://syzkaller.appspot.com/bug?extid=4d9a13f0797c46a29e42
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14172842580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15b04c34580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-53e760d8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/584b4139c7e3/vmlinux-53e760d8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4d2474607300/bzImage-53e760d8.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4d9a13f0797c46a29e42@syzkaller.appspotmail.com

R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000000002
R13: 00007f00d0db5fa0 R14: 00007f00d0db5fa0 R15: 0000000000000005
 </TASK>
------------[ cut here ]------------
WARNING: CPU: 2 PID: 6133 at mm/mremap.c:357 move_normal_pmd mm/mremap.c:357 [inline]
WARNING: CPU: 2 PID: 6133 at mm/mremap.c:357 move_pgt_entry mm/mremap.c:595 [inline]
WARNING: CPU: 2 PID: 6133 at mm/mremap.c:357 move_page_tables+0x3832/0x44a0 mm/mremap.c:852
Modules linked in:
CPU: 2 UID: 0 PID: 6133 Comm: syz.0.19 Not tainted 6.17.0-rc1-syzkaller-00004-g53e760d89498 #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:move_normal_pmd mm/mremap.c:357 [inline]
RIP: 0010:move_pgt_entry mm/mremap.c:595 [inline]
RIP: 0010:move_page_tables+0x3832/0x44a0 mm/mremap.c:852
Code: 02 00 0f 85 b6 03 00 00 48 8b 2b 4c 89 f6 48 89 ef e8 e2 1b af ff 49 39 ee 0f 82 d5 cb ff ff e9 0c cc ff ff e8 1f 21 af ff 90 <0f> 0b 90 48 8b 44 24 40 48 8d 78 40 48 b8 00 00 00 00 00 fc ff df
RSP: 0018:ffffc900037a76d8 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000032930007 RCX: ffffffff820c6645
RDX: ffff88802e56a440 RSI: ffffffff820c7201 RDI: 0000000000000007
RBP: ffff888037728fc0 R08: 0000000000000007 R09: 0000000000000000
R10: 0000000032930007 R11: 0000000000000000 R12: 0000000000000000
R13: ffffc900037a79a8 R14: 0000000000000001 R15: dffffc0000000000
FS:  000055556316a500(0000) GS:ffff8880d68bc000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b30863fff CR3: 0000000050171000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 copy_vma_and_data+0x468/0x790 mm/mremap.c:1215
 move_vma+0x548/0x1780 mm/mremap.c:1282
 mremap_to+0x1b7/0x450 mm/mremap.c:1406
 do_mremap+0xfad/0x1f80 mm/mremap.c:1921
 __do_sys_mremap+0x119/0x170 mm/mremap.c:1977
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f00d0b8ebe9
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:00007ffe5ea5ee98 EFLAGS: 00000246 ORIG_RAX: 0000000000000019
RAX: ffffffffffffffda RBX: 00007f00d0db5fa0 RCX: 00007f00d0b8ebe9
RDX: 0000000000400000 RSI: 0000000000c00000 RDI: 0000200000000000
RBP: 00007ffe5ea5eef0 R08: 0000200000c00000 R09: 0000000000000000
R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000000002
R13: 00007f00d0db5fa0 R14: 00007f00d0db5fa0 R15: 0000000000000005
 </TASK>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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syzbot will keep track of this issue. See:
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If the report is already addressed, let syzbot know by replying with:
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If you want syzbot to run the reproducer, reply with:
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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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If the report is a duplicate of another one, reply with:
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If you want to undo deduplication, reply with:
#syz undup

Re: [syzbot] [mm?] WARNING in move_page_tables

[Lorenzo Stoakes]

On Tue, Aug 12, 2025 at 02:56:35PM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    53e760d89498 Merge tag 'nfsd-6.17-1' of git://git.kernel.o..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=165fe9a2580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f9319a42cfb3bf57
> dashboard link: https://syzkaller.appspot.com/bug?extid=4d9a13f0797c46a29e42
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14172842580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15b04c34580000
>

As usual the repro doesn't repro for me.

Let's try [0] as a quick check as upstream doesn't have it yet.

[0]:https://lore.kernel.org/all/20250806145611.3962-1-dev.jain@arm.com/

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-hotfixes-unstable

> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-53e760d8.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/584b4139c7e3/vmlinux-53e760d8.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/4d2474607300/bzImage-53e760d8.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+4d9a13f0797c46a29e42@syzkaller.appspotmail.com
>
> R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000000002
> R13: 00007f00d0db5fa0 R14: 00007f00d0db5fa0 R15: 0000000000000005
>  </TASK>
> ------------[ cut here ]------------
> WARNING: CPU: 2 PID: 6133 at mm/mremap.c:357 move_normal_pmd mm/mremap.c:357 [inline]
> WARNING: CPU: 2 PID: 6133 at mm/mremap.c:357 move_pgt_entry mm/mremap.c:595 [inline]
> WARNING: CPU: 2 PID: 6133 at mm/mremap.c:357 move_page_tables+0x3832/0x44a0 mm/mremap.c:852
> Modules linked in:
> CPU: 2 UID: 0 PID: 6133 Comm: syz.0.19 Not tainted 6.17.0-rc1-syzkaller-00004-g53e760d89498 #0 PREEMPT(full)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> RIP: 0010:move_normal_pmd mm/mremap.c:357 [inline]
> RIP: 0010:move_pgt_entry mm/mremap.c:595 [inline]
> RIP: 0010:move_page_tables+0x3832/0x44a0 mm/mremap.c:852
> Code: 02 00 0f 85 b6 03 00 00 48 8b 2b 4c 89 f6 48 89 ef e8 e2 1b af ff 49 39 ee 0f 82 d5 cb ff ff e9 0c cc ff ff e8 1f 21 af ff 90 <0f> 0b 90 48 8b 44 24 40 48 8d 78 40 48 b8 00 00 00 00 00 fc ff df
> RSP: 0018:ffffc900037a76d8 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: 0000000032930007 RCX: ffffffff820c6645
> RDX: ffff88802e56a440 RSI: ffffffff820c7201 RDI: 0000000000000007
> RBP: ffff888037728fc0 R08: 0000000000000007 R09: 0000000000000000
> R10: 0000000032930007 R11: 0000000000000000 R12: 0000000000000000
> R13: ffffc900037a79a8 R14: 0000000000000001 R15: dffffc0000000000
> FS:  000055556316a500(0000) GS:ffff8880d68bc000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000001b30863fff CR3: 0000000050171000 CR4: 0000000000352ef0
> Call Trace:
>  <TASK>
>  copy_vma_and_data+0x468/0x790 mm/mremap.c:1215
>  move_vma+0x548/0x1780 mm/mremap.c:1282
>  mremap_to+0x1b7/0x450 mm/mremap.c:1406
>  do_mremap+0xfad/0x1f80 mm/mremap.c:1921
>  __do_sys_mremap+0x119/0x170 mm/mremap.c:1977
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f00d0b8ebe9
> 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:00007ffe5ea5ee98 EFLAGS: 00000246 ORIG_RAX: 0000000000000019
> RAX: ffffffffffffffda RBX: 00007f00d0db5fa0 RCX: 00007f00d0b8ebe9
> RDX: 0000000000400000 RSI: 0000000000c00000 RDI: 0000200000000000
> RBP: 00007ffe5ea5eef0 R08: 0000200000c00000 R09: 0000000000000000
> R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000000002
> R13: 00007f00d0db5fa0 R14: 00007f00d0db5fa0 R15: 0000000000000005
>  </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

Re: [syzbot] [mm?] WARNING in move_page_tables

[syzbot]

Hello,

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

Reported-by: syzbot+4d9a13f0797c46a29e42@syzkaller.appspotmail.com
Tested-by: syzbot+4d9a13f0797c46a29e42@syzkaller.appspotmail.com

Tested on:

commit:         0db9b72d mm/userfaultfd: fix kmap_local LIFO ordering ..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-hotfixes-unstable
console output: https://syzkaller.appspot.com/x/log.txt?x=128fb5a2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2323b2d6038203a5
dashboard link: https://syzkaller.appspot.com/bug?extid=4d9a13f0797c46a29e42
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Note: no patches were applied.
Note: testing is done by a robot and is best-effort only.

Re: [syzbot] [mm?] WARNING in move_page_tables

[Harry Yoo]

On Tue, Aug 12, 2025 at 10:08:02PM -0700, syzbot wrote:
> Hello,
> 
> syzbot has tested the proposed patch and the reproducer did not trigger any issue:
> 
> Reported-by: syzbot+4d9a13f0797c46a29e42@syzkaller.appspotmail.com
> Tested-by: syzbot+4d9a13f0797c46a29e42@syzkaller.appspotmail.com
> 
> Tested on:
> 
> commit:         0db9b72d mm/userfaultfd: fix kmap_local LIFO ordering ..
> git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-hotfixes-unstable
> console output: https://syzkaller.appspot.com/x/log.txt?x=128fb5a2580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=2323b2d6038203a5
> dashboard link: https://syzkaller.appspot.com/bug?extid=4d9a13f0797c46a29e42
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> 
> Note: no patches were applied.
> Note: testing is done by a robot and is best-effort only.

This looks spurious. I was able to reproduce it with the reproducer on
the same commit (the latest mm-hotfixes-unstable).

-- 
Cheers,
Harry / Hyeonggon

Re: [syzbot] [mm?] WARNING in move_page_tables

[Harry Yoo]

On Tue, Aug 12, 2025 at 02:56:35PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    53e760d89498 Merge tag 'nfsd-6.17-1' of git://git.kernel.o..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=165fe9a2580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f9319a42cfb3bf57
> dashboard link: https://syzkaller.appspot.com/bug?extid=4d9a13f0797c46a29e42
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14172842580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15b04c34580000
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-53e760d8.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/584b4139c7e3/vmlinux-53e760d8.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/4d2474607300/bzImage-53e760d8.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+4d9a13f0797c46a29e42@syzkaller.appspotmail.com

[Cc'ing Ryan, Mikołaj, David and Peter]

I was able to reliably reproduce this (with the reproducer provided
by syzbot) and performed bisection.

The first bad commit is 0cef0bb836e mm: clear uffd-wp PTE/PMD state on
mremap(), which was introduced in v6.13.

Adding git bisect log.

# Git bisect log

$ git bisect start
# status: waiting for both good and bad commits
# bad: [19272b37aa4f83ca52bdf9c16d5d81bdd1354494] Linux 6.16-rc1
git bisect bad 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
# status: waiting for good commit(s), bad commit known
# bad: [0ff41df1cb268fc69e703a08a57ee14ae967d0ca] Linux 6.15
git bisect bad 0ff41df1cb268fc69e703a08a57ee14ae967d0ca
# status: waiting for good commit(s), bad commit known
# bad: [38fec10eb60d687e30c8c6b5420d86e8149f7557] Linux 6.14
git bisect bad 38fec10eb60d687e30c8c6b5420d86e8149f7557
# status: waiting for good commit(s), bad commit known
# good: [0c3836482481200ead7b416ca80c68a29cfdaabd] Linux 6.10
git bisect good 0c3836482481200ead7b416ca80c68a29cfdaabd
# good: [77b679453d3364688ff3e5153c0be5b2b52672b7] Merge tag 'v6.12-rc3' into perf-tools-next
git bisect good 77b679453d3364688ff3e5153c0be5b2b52672b7
# good: [77b679453d3364688ff3e5153c0be5b2b52672b7] Merge tag 'v6.12-rc3' into perf-tools-next
git bisect good 77b679453d3364688ff3e5153c0be5b2b52672b7
# good: [05d5d3840b2d52619ffb79e60ab58e30a7f86037] Merge branches '20241204-sm8750_master_clks-v3-0-1a8f31a53a86@quicinc.com' and '20250106-sm8750-dispcc-v2-1-6f42beda6317@linaro.org' into arm64-for-6.14
git bisect good 05d5d3840b2d52619ffb79e60ab58e30a7f86037
# good: [05d5d3840b2d52619ffb79e60ab58e30a7f86037] Merge branches '20241204-sm8750_master_clks-v3-0-1a8f31a53a86@quicinc.com' and '20250106-sm8750-dispcc-v2-1-6f42beda6317@linaro.org' into arm64-for-6.14
git bisect good 05d5d3840b2d52619ffb79e60ab58e30a7f86037
# bad: [d0d106a2bd21499901299160744e5fe9f4c83ddb] Merge tag 'bpf-next-6.14' of git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next
git bisect bad d0d106a2bd21499901299160744e5fe9f4c83ddb
# bad: [d0d106a2bd21499901299160744e5fe9f4c83ddb] Merge tag 'bpf-next-6.14' of git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next
git bisect bad d0d106a2bd21499901299160744e5fe9f4c83ddb
# good: [4f1a62e2b3961946a924c093bc2bdd44a2a46c9d] dt-bindings: clock: qcom,sm8550-dispcc: Add SM8750 DISPCC
git bisect good 4f1a62e2b3961946a924c093bc2bdd44a2a46c9d
# good: [8817c21a45b62c17f18417efbd0b04a3805a1e23] dt-bindings: clock: qcom: Document the SM8750 TCSR Clock Controller
git bisect good 8817c21a45b62c17f18417efbd0b04a3805a1e23
# good: [f4d3d7340e719dd3d2c23ce8d6c360e2f93ba7e4] dt-bindings: clock: qcom: Add QCS615 GCC clocks
git bisect good f4d3d7340e719dd3d2c23ce8d6c360e2f93ba7e4
# good: [f4d3d7340e719dd3d2c23ce8d6c360e2f93ba7e4] dt-bindings: clock: qcom: Add QCS615 GCC clocks
git bisect good f4d3d7340e719dd3d2c23ce8d6c360e2f93ba7e4
# bad: [cf33d96f50903214226b379b3f10d1f262dae018] Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
git bisect bad cf33d96f50903214226b379b3f10d1f262dae018
# good: [a603abe345d6301f04dc2ceb5fbdaa19e4c8f7da] Merge tag 'perf_urgent_for_v6.13_rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
git bisect good a603abe345d6301f04dc2ceb5fbdaa19e4c8f7da
# good: [79f4b6934dbd7dd6741726ba004a15e25380b8cc] wifi: iwlwifi: mvm: remove unneeded NULL pointer checks
git bisect good 79f4b6934dbd7dd6741726ba004a15e25380b8cc
# bad: [2ee738e90e80850582cbe10f34c6447965c1d87b] Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
git bisect bad 2ee738e90e80850582cbe10f34c6447965c1d87b
# good: [bc1e64d5403d7926a3d79fdbbdf628b69f0939a2] Merge branch 'net-use-netdev-lock-to-protect-napi'
git bisect good bc1e64d5403d7926a3d79fdbbdf628b69f0939a2
# good: [3744b08449c27bfa085aa218c4830f3996a51626] Merge branch 'pm-cpufreq'
git bisect good 3744b08449c27bfa085aa218c4830f3996a51626
# good: [a50da36562cd62b41de9bef08edbb3e8af00f118] netdev: avoid CFI problems with sock priv helpers
git bisect good a50da36562cd62b41de9bef08edbb3e8af00f118
# bad: [79a1d390f879563119bf2848b621bc7eed228c7d] Merge tag 'sound-6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound
git bisect bad 79a1d390f879563119bf2848b621bc7eed228c7d
# bad: [cbc5dde0a461240046e8a41c43d7c3b76d5db952] fs/proc: fix softlockup in __read_vmcore (part 2)
git bisect bad cbc5dde0a461240046e8a41c43d7c3b76d5db952
# good: [4dff389c9f1dd787e8058930b3fbd3248a6238c5] Revert "mm: zswap: fix race between [de]compression and CPU hotunplug"
git bisect good 4dff389c9f1dd787e8058930b3fbd3248a6238c5
# bad: [a32bf5bb7933fde6f39747499f8ec232b5b5400f] selftests/mm: set allocated memory to non-zero content in cow test
git bisect bad a32bf5bb7933fde6f39747499f8ec232b5b5400f
# good: [4bcf29741145e73440323e3e9af8b1a6f4961183] module: fix writing of livepatch relocations in ROX text
git bisect good 4bcf29741145e73440323e3e9af8b1a6f4961183
# bad: [0cef0bb836e3cfe00f08f9606c72abd72fe78ca3] mm: clear uffd-wp PTE/PMD state on mremap()
git bisect bad 0cef0bb836e3cfe00f08f9606c72abd72fe78ca3
# first bad commit: [0cef0bb836e3cfe00f08f9606c72abd72fe78ca3] mm: clear uffd-wp PTE/PMD state on mremap()

-- 
Cheers,
Harry / Hyeonggon

> R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000000002
> R13: 00007f00d0db5fa0 R14: 00007f00d0db5fa0 R15: 0000000000000005
>  </TASK>
> ------------[ cut here ]------------
> WARNING: CPU: 2 PID: 6133 at mm/mremap.c:357 move_normal_pmd mm/mremap.c:357 [inline]
> WARNING: CPU: 2 PID: 6133 at mm/mremap.c:357 move_pgt_entry mm/mremap.c:595 [inline]
> WARNING: CPU: 2 PID: 6133 at mm/mremap.c:357 move_page_tables+0x3832/0x44a0 mm/mremap.c:852
> Modules linked in:
> CPU: 2 UID: 0 PID: 6133 Comm: syz.0.19 Not tainted 6.17.0-rc1-syzkaller-00004-g53e760d89498 #0 PREEMPT(full) 
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> RIP: 0010:move_normal_pmd mm/mremap.c:357 [inline]
> RIP: 0010:move_pgt_entry mm/mremap.c:595 [inline]
> RIP: 0010:move_page_tables+0x3832/0x44a0 mm/mremap.c:852
> Code: 02 00 0f 85 b6 03 00 00 48 8b 2b 4c 89 f6 48 89 ef e8 e2 1b af ff 49 39 ee 0f 82 d5 cb ff ff e9 0c cc ff ff e8 1f 21 af ff 90 <0f> 0b 90 48 8b 44 24 40 48 8d 78 40 48 b8 00 00 00 00 00 fc ff df
> RSP: 0018:ffffc900037a76d8 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: 0000000032930007 RCX: ffffffff820c6645
> RDX: ffff88802e56a440 RSI: ffffffff820c7201 RDI: 0000000000000007
> RBP: ffff888037728fc0 R08: 0000000000000007 R09: 0000000000000000
> R10: 0000000032930007 R11: 0000000000000000 R12: 0000000000000000
> R13: ffffc900037a79a8 R14: 0000000000000001 R15: dffffc0000000000
> FS:  000055556316a500(0000) GS:ffff8880d68bc000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000001b30863fff CR3: 0000000050171000 CR4: 0000000000352ef0
> Call Trace:
>  <TASK>
>  copy_vma_and_data+0x468/0x790 mm/mremap.c:1215
>  move_vma+0x548/0x1780 mm/mremap.c:1282
>  mremap_to+0x1b7/0x450 mm/mremap.c:1406
>  do_mremap+0xfad/0x1f80 mm/mremap.c:1921
>  __do_sys_mremap+0x119/0x170 mm/mremap.c:1977
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f00d0b8ebe9
> 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:00007ffe5ea5ee98 EFLAGS: 00000246 ORIG_RAX: 0000000000000019
> RAX: ffffffffffffffda RBX: 00007f00d0db5fa0 RCX: 00007f00d0b8ebe9
> RDX: 0000000000400000 RSI: 0000000000c00000 RDI: 0000200000000000
> RBP: 00007ffe5ea5eef0 R08: 0000200000c00000 R09: 0000000000000000
> R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000000002
> R13: 00007f00d0db5fa0 R14: 00007f00d0db5fa0 R15: 0000000000000005
>  </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
> 

Re: [syzbot] [mm?] WARNING in move_page_tables

[David Hildenbrand]

On 13.08.25 14:20, Harry Yoo wrote:
> On Tue, Aug 12, 2025 at 02:56:35PM -0700, syzbot wrote:
>> Hello,
>>
>> syzbot found the following issue on:
>>
>> HEAD commit:    53e760d89498 Merge tag 'nfsd-6.17-1' of git://git.kernel.o..
>> git tree:       upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=165fe9a2580000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=f9319a42cfb3bf57
>> dashboard link: https://syzkaller.appspot.com/bug?extid=4d9a13f0797c46a29e42
>> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14172842580000
>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15b04c34580000
>>
>> Downloadable assets:
>> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-53e760d8.raw.xz
>> vmlinux: https://storage.googleapis.com/syzbot-assets/584b4139c7e3/vmlinux-53e760d8.xz
>> kernel image: https://storage.googleapis.com/syzbot-assets/4d2474607300/bzImage-53e760d8.xz
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+4d9a13f0797c46a29e42@syzkaller.appspotmail.com
> 
> [Cc'ing Ryan, Mikołaj, David and Peter]
> 
> I was able to reliably reproduce this (with the reproducer provided
> by syzbot) and performed bisection.
> 
> The first bad commit is 0cef0bb836e mm: clear uffd-wp PTE/PMD state on
> mremap(), which was introduced in v6.13.
> 


Okay, so we're hitting the

	if (WARN_ON_ONCE(!pmd_none(*new_pmd)))
		return false;

in move_normal_pmd().

Given that the reproducer involves allocation fault injection during move_page_tables(),
I assume we run into this warning when we are trying to restore our previous state,
so when we call move_page_tables() the
second time from copy_vma_and_data().

Something when moving stuff back after a failed PTE table allocation is broken.


Ah, maybe I know what happens.

When we move the first time, we check "vma_has_uffd_without_event_remap(orig_vma)"
and see that "yes, this thing has uffd" and decide to move PTE level

When we move back, we check "vma_has_uffd_without_event_remap(new_vma)" and see
that "no, this thing does not have uffd" and decide to move PMD level.

But the original PTE table is still there ...

As a side-note: It's confusing to call vma_has_uffd_without_event_remap() to make
a decision during mremap to handle WP, when WP might not even be active.
We should likely slap in a uffd-wp check on the VMA as a follow-up cleanup.

#syz test

diff --git a/mm/mremap.c b/mm/mremap.c
index 33b642076205d..a9730f4373b77 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -323,6 +323,26 @@ static inline bool arch_supports_page_table_move(void)
  }
  #endif
  
+static inline bool uffd_supports_page_table_move(struct pagetable_move_control *pmc)
+{
+	/*
+	 * If we are moving VMAs that have uffd-wp registered but with
+	 * remap events disabled (new VMA will not be registered with uffd), we
+	 * need to ensure that the uffd-wp state is cleared from all pgtables.
+	 * This means recursing into lower page tables in move_page_tables().
+	 *
+	 * We setup the uffd-wp context on the new VMA after moving the page
+	 * tables succeeded, so checking the old VMA looks reasonable. However,
+	 * when we have to recover from a failed page table move attempt, we
+	 * get called with inverse VMAs. Recursing into lower page tables during
+	 * the original move but not during the recovery move will cause
+	 * trouble, because we run into already-existing page tables during
+	 * the recovery phase. Consequently, check both VMAs.
+	 */
+	return !vma_has_uffd_without_event_remap(pmc->old) &&
+	       !vma_has_uffd_without_event_remap(pmc->new);
+}
+
  #ifdef CONFIG_HAVE_MOVE_PMD
  static bool move_normal_pmd(struct pagetable_move_control *pmc,
  			pmd_t *old_pmd, pmd_t *new_pmd)
@@ -335,6 +355,8 @@ static bool move_normal_pmd(struct pagetable_move_control *pmc,
  
  	if (!arch_supports_page_table_move())
  		return false;
+	if (!uffd_supports_page_table_move(pmc))
+		return false;
  	/*
  	 * The destination pmd shouldn't be established, free_pgtables()
  	 * should have released it.
@@ -361,15 +383,6 @@ static bool move_normal_pmd(struct pagetable_move_control *pmc,
  	if (WARN_ON_ONCE(!pmd_none(*new_pmd)))
  		return false;
  
-	/* If this pmd belongs to a uffd vma with remap events disabled, we need
-	 * to ensure that the uffd-wp state is cleared from all pgtables. This
-	 * means recursing into lower page tables in move_page_tables(), and we
-	 * can reuse the existing code if we simply treat the entry as "not
-	 * moved".
-	 */
-	if (vma_has_uffd_without_event_remap(vma))
-		return false;
-
  	/*
  	 * We don't have to worry about the ordering of src and dst
  	 * ptlocks because exclusive mmap_lock prevents deadlock.
@@ -418,6 +431,8 @@ static bool move_normal_pud(struct pagetable_move_control *pmc,
  
  	if (!arch_supports_page_table_move())
  		return false;
+	if (!uffd_supports_page_table_move(pmc))
+		return false;
  	/*
  	 * The destination pud shouldn't be established, free_pgtables()
  	 * should have released it.
@@ -425,15 +440,6 @@ static bool move_normal_pud(struct pagetable_move_control *pmc,
  	if (WARN_ON_ONCE(!pud_none(*new_pud)))
  		return false;
  
-	/* If this pud belongs to a uffd vma with remap events disabled, we need
-	 * to ensure that the uffd-wp state is cleared from all pgtables. This
-	 * means recursing into lower page tables in move_page_tables(), and we
-	 * can reuse the existing code if we simply treat the entry as "not
-	 * moved".
-	 */
-	if (vma_has_uffd_without_event_remap(vma))
-		return false;
-
  	/*
  	 * We don't have to worry about the ordering of src and dst
  	 * ptlocks because exclusive mmap_lock prevents deadlock.
-- 
2.50.1

-- 
Cheers

David / dhildenb

Re: [syzbot] [mm?] WARNING in move_page_tables

[syzbot]

Hello,

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

failed to apply patch:
checking file mm/mremap.c
Hunk #1 FAILED at 323.
1 out of 5 hunks FAILED



Tested on:

commit:         c17b750b Linux 6.17-rc2
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=f9319a42cfb3bf57
dashboard link: https://syzkaller.appspot.com/bug?extid=4d9a13f0797c46a29e42
compiler:       
patch:          https://syzkaller.appspot.com/x/patch.diff?x=107dbba2580000

Re: [syzbot] [mm?] WARNING in move_page_tables

[David Hildenbrand]

On 18.08.25 14:56, syzbot wrote:
> Hello,
> 
> syzbot tried to test the proposed patch but the build/boot failed:
> 
> failed to apply patch:
> checking file mm/mremap.c
> Hunk #1 FAILED at 323.
> 1 out of 5 hunks FAILED
> 

#syz test https://github.com/davidhildenbrand/linux.git uffd-wp

-- 
Cheers

David / dhildenb

Re: [syzbot] [mm?] WARNING in move_page_tables

[syzbot]

Hello,

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

Reported-by: syzbot+4d9a13f0797c46a29e42@syzkaller.appspotmail.com
Tested-by: syzbot+4d9a13f0797c46a29e42@syzkaller.appspotmail.com

Tested on:

commit:         eaa49d2c tmp
git tree:       https://github.com/davidhildenbrand/linux.git uffd-wp
console output: https://syzkaller.appspot.com/x/log.txt?x=151c5234580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=247d4d29e685f61c
dashboard link: https://syzkaller.appspot.com/bug?extid=4d9a13f0797c46a29e42
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Note: no patches were applied.
Note: testing is done by a robot and is best-effort only.