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KCSAN: data-race in munlock_folio / need_mlock_drain (8)

Status: moderation: reported on 2026/02/21 02:12
Subsystems: mm
[Documentation on labels]
Reported-by: syzbot+33db640519d6c4bdeebc@syzkaller.appspotmail.com
First crash: 6d17h, last: 6d17h
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
c7c9f9ed-4907-4c3f-9d8f-0f2658ebc940 assessment-kcsan Benign: ✅  Confident: ✅  KCSAN: data-race in munlock_folio / need_mlock_drain (8) 2026/02/23 14:36 2026/02/23 14:36 2026/02/23 14:47 305c0ec5cd886e2d13738e28e1b2df9b0ec20fc9
Similar bugs (7)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in munlock_folio / need_mlock_drain mm 6 1 1032d 1032d 0/29 auto-obsoleted due to no activity on 2023/06/05 22:24
upstream KCSAN: data-race in munlock_folio / need_mlock_drain (2) mm 6 1 878d 878d 0/29 auto-obsoleted due to no activity on 2023/11/07 10:03
upstream KCSAN: data-race in munlock_folio / need_mlock_drain (5) mm 6 16 479d 635d 0/29 auto-obsoleted due to no activity on 2024/12/31 00:27
upstream KCSAN: data-race in munlock_folio / need_mlock_drain (4) mm 6 1 672d 672d 0/29 auto-obsoleted due to no activity on 2024/05/31 11:19
upstream KCSAN: data-race in munlock_folio / need_mlock_drain (6) mm 6 7 299d 397d 0/29 auto-obsoleted due to no activity on 2025/06/29 06:03
upstream KCSAN: data-race in munlock_folio / need_mlock_drain (7) mm 6 5 80d 230d 0/29 auto-obsoleted due to no activity on 2026/02/03 07:01
upstream KCSAN: data-race in munlock_folio / need_mlock_drain (3) mm 6 2 774d 803d 0/29 auto-obsoleted due to no activity on 2024/02/18 23:01

Sample crash report:
EXT4-fs (loop7): unmounting filesystem 00000000-0000-0000-0000-000000000000.
==================================================================
BUG: KCSAN: data-race in munlock_folio / need_mlock_drain

read-write to 0xffff888237d27210 of 1 bytes by task 8974 on cpu 1:
 folio_batch_add include/linux/pagevec.h:77 [inline]
 munlock_folio+0x44/0x120 mm/mlock.c:301
 munlock_vma_folio mm/internal.h:1140 [inline]
 __folio_remove_rmap mm/rmap.c:1870 [inline]
 folio_remove_rmap_ptes+0x197/0x1a0 mm/rmap.c:1887
 zap_present_folio_ptes mm/memory.c:1667 [inline]
 zap_present_ptes mm/memory.c:1725 [inline]
 do_zap_pte_range mm/memory.c:1827 [inline]
 zap_pte_range mm/memory.c:1929 [inline]
 zap_pmd_range mm/memory.c:2021 [inline]
 zap_pud_range mm/memory.c:2049 [inline]
 zap_p4d_range mm/memory.c:2070 [inline]
 unmap_page_range+0x1752/0x2e80 mm/memory.c:2091
 unmap_single_vma mm/memory.c:2133 [inline]
 unmap_vmas+0x2ba/0x420 mm/memory.c:2171
 exit_mmap+0x1ab/0x620 mm/mmap.c:1302
 __mmput+0x28/0x1c0 kernel/fork.c:1174
 mmput+0x40/0x50 kernel/fork.c:1197
 exit_mm+0xe3/0x180 kernel/exit.c:581
 do_exit+0x3fa/0x15a0 kernel/exit.c:959
 do_group_exit+0x138/0x140 kernel/exit.c:1112
 __do_sys_exit_group kernel/exit.c:1123 [inline]
 __se_sys_exit_group kernel/exit.c:1121 [inline]
 __x64_sys_exit_group+0x1f/0x20 kernel/exit.c:1121
 x64_sys_call+0x3008/0x3020 arch/x86/include/generated/asm/syscalls_64.h:232
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888237d27210 of 1 bytes by task 7352 on cpu 0:
 folio_batch_count include/linux/pagevec.h:56 [inline]
 need_mlock_drain+0x30/0x50 mm/mlock.c:235
 cpu_needs_drain mm/swap.c:786 [inline]
 __lru_add_drain_all+0x273/0x450 mm/swap.c:877
 lru_add_drain_all+0x10/0x20 mm/swap.c:893
 invalidate_bdev+0x47/0x70 block/bdev.c:101
 ext4_put_super+0x624/0x7d0 fs/ext4/super.c:1353
 generic_shutdown_super+0xee/0x220 fs/super.c:646
 kill_block_super+0x2a/0x70 fs/super.c:1725
 ext4_kill_sb+0x42/0x80 fs/ext4/super.c:7461
 deactivate_locked_super+0x75/0x1c0 fs/super.c:476
 deactivate_super+0x97/0xa0 fs/super.c:509
 cleanup_mnt+0x2bb/0x330 fs/namespace.c:1312
 __cleanup_mnt+0x19/0x20 fs/namespace.c:1319
 task_work_run+0x130/0x1a0 kernel/task_work.c:233
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 __exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
 exit_to_user_mode_loop+0x1f4/0x6f0 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
 do_syscall_64+0x249/0x370 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x14 -> 0x1f

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 7352 Comm: syz-executor Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/02/21 02:11 upstream a95f71ad3e2e 6e7b5511 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in munlock_folio / need_mlock_drain
* Struck through repros no longer work on HEAD.