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([2001:1a48:8:903:1ed6:4f73:ce38:f9d4]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-486f4b89d87sm81564425e9.6.2026.03.19.03.56.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Mar 2026 03:56:22 -0700 (PDT) Message-ID: <5eaa234e-76e5-45ec-833d-64d76903d1bf@suse.com> Date: Thu, 19 Mar 2026 11:56:21 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [syzbot] [mm?] kernel BUG in collapse_scan_file Content-Language: en-US To: Lance Yang , syzbot , david@kernel.org, ljs@kernel.org, willy@infradead.org, Mark Brown Cc: baolin.wang@linux.alibaba.com, npache@redhat.com, linux-mm@kvack.org, baohua@kernel.org, ryan.roberts@arm.com, syzkaller-bugs@googlegroups.com, dev.jain@arm.com, ziy@nvidia.com, linux-kernel@vger.kernel.org, Liam.Howlett@oracle.com, akpm@linux-foundation.org References: <69bba3c0.050a0220.227207.002b.GAE@google.com> From: Vlastimil Babka In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/19/26 09:05, Lance Yang wrote: > Ccing Willy > > IIUC, this is a dup of the earlier report[1], which I looked into back > in January. The root cause is the same: collapse_file() calls > xas_lock_irq() without resetting the xas state first, tripping the > XAS_INVALID() assertion: > > #define xas_lock_irq(xas) xa_lock_irq(XAS_INVALID(xas)->xa) > > static inline struct xa_state *XAS_INVALID(struct xa_state *xas) > { > XA_NODE_BUG_ON(xas->xa_node, xas_valid(xas)); > return xas; > } > > Added by commit: > > commit 43b00759f21b10142094d1ae5ff65cbb368953a3 > Author: Matthew Wilcox (Oracle) > Date: Sun Dec 14 10:53:31 2025 -0500 > > XArray: Add extra debugging check to xas_lock and friends > > While tracking down a recent bug, we discovered somewhere that had > forgotten to call xas_reset() before calling xas_lock(). Add a debug > check to be sure that doesn't happen in future and fix all the > places in > the test suite which were carelessly doing just this. > > Suggested-by: Linus Torvalds > Signed-off-by: Matthew Wilcox (Oracle) > > I posted a HACK fix at the time[2], but David pointed out that Willy > had mentioned it likely needs more thought[3]. > > [1] > https://lore.kernel.org/all/69757ea0.a00a0220.33ccc7.0017.GAE@google.com/ > [2] https://lore.kernel.org/all/20260125121001.32733-1-lance.yang@linux.dev/ > [3] > https://lore.kernel.org/all/7bce9231-714c-424a-a4e3-dd42734fb767@kernel.org/ That "needs more thought" was Jan 5. After 2.5 months later this is still messing up linux-next testing due to a known unfixed problem. Completely unnaceptable. Willy, you need to drop the new bug check until the known problem is fixed. Mark, please drop https://git.infradead.org/users/willy/xarray.git from linux-next until it stops breaking linux-next. Thanks. > > Thanks, > Lance > > > On 2026/3/19 15:20, syzbot wrote: >> Hello, >> >> syzbot found the following issue on: >> >> HEAD commit: 95c541ddfb08 Add linux-next specific files for 20260316 >> git tree: linux-next >> console output: https://syzkaller.appspot.com/x/log.txt?x=15ccc216580000 >> kernel config: https://syzkaller.appspot.com/x/.config?x=ed431987028345c6 >> dashboard link: https://syzkaller.appspot.com/bug?extid=8961cb270ae74b4129fb >> compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8 >> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12f778da580000 >> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12cc006a580000 >> >> Downloadable assets: >> disk image: https://storage.googleapis.com/syzbot-assets/c40f27ad73d8/disk-95c541dd.raw.xz >> vmlinux: https://storage.googleapis.com/syzbot-assets/bd811888f684/vmlinux-95c541dd.xz >> kernel image: https://storage.googleapis.com/syzbot-assets/3b72363d7dbd/bzImage-95c541dd.xz >> >> IMPORTANT: if you fix the issue, please add the following tag to the commit: >> Reported-by: syzbot+8961cb270ae74b4129fb@syzkaller.appspotmail.com >> >> node ffff88805d558b00 offset 0 parent ffff88805d558840 shift 0 count 3 values 0 array ffff88807a8195c0 list ffff88805d558b18 ffff88805d558b18 marks 0 0 0 >> ------------[ cut here ]------------ >> kernel BUG at ./include/linux/xarray.h:1441! >> Oops: invalid opcode: 0000 [#1] SMP KASAN PTI >> CPU: 0 UID: 0 PID: 6001 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026 >> RIP: 0010:XAS_INVALID include/linux/xarray.h:1441 [inline] >> RIP: 0010:collapse_file mm/khugepaged.c:2055 [inline] >> RIP: 0010:collapse_scan_file+0x4f98/0x5230 mm/khugepaged.c:2404 >> Code: ff 4c 89 e7 48 c7 c6 60 b2 dc 8b e8 82 62 f1 fe 90 0f 0b 48 85 db 0f 84 03 01 00 00 e8 71 e5 8f ff 48 89 df e8 a9 20 7b 09 90 <0f> 0b e8 61 e5 8f ff 48 89 df 48 c7 c6 60 b2 dc 8b e8 52 62 f1 fe >> RSP: 0018:ffffc90003826e20 EFLAGS: 00010246 >> RAX: 0000000000000000 RBX: ffff88805d558b00 RCX: a13f20bd39c5a100 >> RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000 >> RBP: ffffc90003827130 R08: ffffc90003826ba7 R09: 1ffff92000704d74 >> R10: dffffc0000000000 R11: fffff52000704d75 R12: ffffea0001b678f0 >> R13: dffffc0000000000 R14: 0000000000000000 R15: ffffc90003827010 >> FS: 000055557e3c2500(0000) GS:ffff888125437000(0000) knlGS:0000000000000000 >> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> CR2: 000020000000b000 CR3: 000000007ac66000 CR4: 00000000003526f0 >> Call Trace: >> >> collapse_single_pmd+0x22b/0x4510 mm/khugepaged.c:2437 >> madvise_collapse+0x34c/0x820 mm/khugepaged.c:2859 >> madvise_vma_behavior+0x1094/0x4460 mm/madvise.c:1362 >> madvise_walk_vmas+0x573/0xae0 mm/madvise.c:1711 >> madvise_do_behavior+0x386/0x540 mm/madvise.c:1927 >> do_madvise+0x1fa/0x2e0 mm/madvise.c:2020 >> __do_sys_madvise mm/madvise.c:2029 [inline] >> __se_sys_madvise mm/madvise.c:2027 [inline] >> __x64_sys_madvise+0xa6/0xc0 mm/madvise.c:2027 >> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] >> do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94 >> entry_SYSCALL_64_after_hwframe+0x77/0x7f >> RIP: 0033:0x7f90d419c799 >> Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48 >> RSP: 002b:00007ffd50711398 EFLAGS: 00000246 ORIG_RAX: 000000000000001c >> RAX: ffffffffffffffda RBX: 00007f90d4415fa0 RCX: 00007f90d419c799 >> RDX: 0000000000000019 RSI: 0000000000600003 RDI: 0000200000000000 >> RBP: 00007f90d4232c99 R08: 0000000000000000 R09: 0000000000000000 >> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 >> R13: 00007f90d4415fac R14: 00007f90d4415fa0 R15: 00007f90d4415fa0 >> >> Modules linked in: >> ---[ end trace 0000000000000000 ]--- >> RIP: 0010:XAS_INVALID include/linux/xarray.h:1441 [inline] >> RIP: 0010:collapse_file mm/khugepaged.c:2055 [inline] >> RIP: 0010:collapse_scan_file+0x4f98/0x5230 mm/khugepaged.c:2404 >> Code: ff 4c 89 e7 48 c7 c6 60 b2 dc 8b e8 82 62 f1 fe 90 0f 0b 48 85 db 0f 84 03 01 00 00 e8 71 e5 8f ff 48 89 df e8 a9 20 7b 09 90 <0f> 0b e8 61 e5 8f ff 48 89 df 48 c7 c6 60 b2 dc 8b e8 52 62 f1 fe >> RSP: 0018:ffffc90003826e20 EFLAGS: 00010246 >> RAX: 0000000000000000 RBX: ffff88805d558b00 RCX: a13f20bd39c5a100 >> RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000 >> RBP: ffffc90003827130 R08: ffffc90003826ba7 R09: 1ffff92000704d74 >> R10: dffffc0000000000 R11: fffff52000704d75 R12: ffffea0001b678f0 >> R13: dffffc0000000000 R14: 0000000000000000 R15: ffffc90003827010 >> FS: 000055557e3c2500(0000) GS:ffff888125537000(0000) knlGS:0000000000000000 >> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> CR2: 00007f8156602000 CR3: 000000007ac66000 CR4: 00000000003526f0 >> >> >> --- >> 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 > >