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From: Lance Yang Date: Fri, 26 Sep 2025 17:35:48 +0800 X-Gmail-Original-Message-ID: X-Gm-Features: AS18NWBk7yoZQ6JxZ96p9n__yfVmWuL-V3XgGu7UllO4xRF8xd7eIwb3A-ueoC8 Message-ID: Subject: Re: [syzbot] [mm?] KCSAN: data-race in try_to_migrate_one / zap_page_range_single_batched To: Marco Elver Cc: syzbot , Liam.Howlett@oracle.com, akpm@linux-foundation.org, david@redhat.com, harry.yoo@oracle.com, jannh@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, riel@surriel.com, syzkaller-bugs@googlegroups.com, vbabka@suse.cz Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 312CA140006 X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: cqm47t53brth9wx7oj83oqju64r38xm3 X-HE-Tag: 1758879390-987546 X-HE-Meta: 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List-Unsubscribe: On Fri, Sep 26, 2025 at 2:55=E2=80=AFPM Marco Elver wrot= e: > > On Fri, 26 Sept 2025 at 08:44, syzbot > wrote: > > > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: cec1e6e5d1ab Merge tag 'sched_ext-for-6.17-rc7-fixes' o= f g.. > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=3D145d4f12580= 000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=3D6e0c213d073= 5f5dd > > dashboard link: https://syzkaller.appspot.com/bug?extid=3D60192c8877d0b= c92a92b > > compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7= 976-1~exp1~20250708183702.136), Debian LLD 20.1.8 > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > Downloadable assets: > > disk image: https://storage.googleapis.com/syzbot-assets/10b7c8fdfdec/d= isk-cec1e6e5.raw.xz > > vmlinux: https://storage.googleapis.com/syzbot-assets/cbecc36962db/vmli= nux-cec1e6e5.xz > > kernel image: https://storage.googleapis.com/syzbot-assets/214f107d0a3e= /bzImage-cec1e6e5.xz > > > > IMPORTANT: if you fix the issue, please add the following tag to the co= mmit: > > Reported-by: syzbot+60192c8877d0bc92a92b@syzkaller.appspotmail.com > > > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > BUG: KCSAN: data-race in try_to_migrate_one / zap_page_range_single_bat= ched > > > > write to 0xffff88810adfd798 of 8 bytes by task 13594 on cpu 1: > > update_hiwater_rss include/linux/mm.h:2657 [inline] > > try_to_migrate_one+0x918/0x16e0 mm/rmap.c:2455 > > __rmap_walk_file+0x1ec/0x2b0 mm/rmap.c:2905 > > try_to_migrate+0x1db/0x210 mm/rmap.c:-1 > > migrate_folio_unmap mm/migrate.c:1324 [inline] > > migrate_pages_batch+0x6e1/0x1ae0 mm/migrate.c:1873 > > migrate_pages_sync mm/migrate.c:1996 [inline] > > migrate_pages+0xf5f/0x1770 mm/migrate.c:2105 > > do_mbind mm/mempolicy.c:1539 [inline] > > kernel_mbind mm/mempolicy.c:1682 [inline] > > __do_sys_mbind mm/mempolicy.c:1756 [inline] > > __se_sys_mbind+0x975/0xac0 mm/mempolicy.c:1752 > > __x64_sys_mbind+0x78/0x90 mm/mempolicy.c:1752 > > x64_sys_call+0x2932/0x2ff0 arch/x86/include/generated/asm/syscalls_64.= h:238 > > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] > > do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94 > > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > > > write to 0xffff88810adfd798 of 8 bytes by task 13595 on cpu 0: > > update_hiwater_rss include/linux/mm.h:2657 [inline] > > zap_page_range_single_batched+0x182/0x450 mm/memory.c:2007 > > zap_page_range_single mm/memory.c:2041 [inline] > > unmap_mapping_range_vma mm/memory.c:4020 [inline] > > unmap_mapping_range_tree+0xfd/0x160 mm/memory.c:4037 > > unmap_mapping_pages mm/memory.c:4103 [inline] > > unmap_mapping_range+0xe4/0xf0 mm/memory.c:4140 > > shmem_fallocate+0x262/0x840 mm/shmem.c:3746 > > vfs_fallocate+0x3b6/0x400 fs/open.c:342 > > madvise_remove mm/madvise.c:1049 [inline] > > madvise_vma_behavior+0x192d/0x1cf0 mm/madvise.c:1346 > > madvise_walk_vmas mm/madvise.c:1669 [inline] > > madvise_do_behavior+0x5b7/0x970 mm/madvise.c:1885 > > do_madvise+0x10e/0x190 mm/madvise.c:1978 > > __do_sys_madvise mm/madvise.c:1987 [inline] > > __se_sys_madvise mm/madvise.c:1985 [inline] > > __x64_sys_madvise+0x64/0x80 mm/madvise.c:1985 > > x64_sys_call+0x1f1a/0x2ff0 arch/x86/include/generated/asm/syscalls_64.= h:29 > > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] > > do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94 > > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > > > value changed: 0x0000000000001645 -> 0x0000000000002165 > > One of these writes is getting lost. Which means highwater_rss is > lossy/approximate - does it matter? Yes. IMO, hiwater_rss being lossy is an acceptable trade-off for a non-critical accounting value. The patch[1] simply silences the KCSAN warni= ng. [1] https://lore.kernel.org/linux-mm/20250926092426.43312-1-lance.yang@linu= x.dev/