On Sun, Sep 11, 2022 at 9:27 PM syzbot <syzbot+915f3e317adb0e85835f@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > syzbot has found a reproducer for the following issue on: > > HEAD commit: e47eb90a0a9a Add linux-next specific files for 20220901 > git tree: linux-next > console+strace: https://syzkaller.appspot.com/x/log.txt?x=17330430880000 > kernel config: https://syzkaller.appspot.com/x/.config?x=7933882276523081 > dashboard link: https://syzkaller.appspot.com/bug?extid=915f3e317adb0e85835f > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13397b77080000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1793564f080000 > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+915f3e317adb0e85835f@xxxxxxxxxxxxxxxxxxxxxxxxx > > BUG: Bad page map in process syz-executor198 pte:8000000071c00227 pmd:74b30067 > addr:0000000020563000 vm_flags:08100077 anon_vma:ffff8880547d2200 mapping:0000000000000000 index:20563 > file:(null) fault:0x0 mmap:0x0 read_folio:0x0 > CPU: 1 PID: 3614 Comm: syz-executor198 Not tainted 6.0.0-rc3-next-20220901-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2022 > Call Trace: > <TASK> > __dump_stack lib/dump_stack.c:88 [inline] > dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106 > print_bad_pte.cold+0x2a7/0x2d0 mm/memory.c:565 > vm_normal_page+0x10c/0x2a0 mm/memory.c:636 > hpage_collapse_scan_pmd+0x729/0x1da0 mm/khugepaged.c:1199 > madvise_collapse+0x481/0x910 mm/khugepaged.c:2433 > madvise_vma_behavior+0xd0a/0x1cc0 mm/madvise.c:1062 > madvise_walk_vmas+0x1c7/0x2b0 mm/madvise.c:1236 > do_madvise.part.0+0x24a/0x340 mm/madvise.c:1415 > do_madvise mm/madvise.c:1428 [inline] > __do_sys_madvise mm/madvise.c:1428 [inline] > __se_sys_madvise mm/madvise.c:1426 [inline] > __x64_sys_madvise+0x113/0x150 mm/madvise.c:1426 > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > RIP: 0033:0x7f770ba87929 > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 15 00 00 90 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 b8 ff ff ff f7 d8 64 89 01 48 > RSP: 002b:00007f770ba18308 EFLAGS: 00000246 ORIG_RAX: 000000000000001c > RAX: ffffffffffffffda RBX: 00007f770bb0f3f8 RCX: 00007f770ba87929 > RDX: 0000000000000019 RSI: 0000000000600003 RDI: 0000000020000000 > RBP: 00007f770bb0f3f0 R08: 00007f770ba18700 R09: 0000000000000000 > R10: 00007f770ba18700 R11: 0000000000000246 R12: 00007f770bb0f3fc > R13: 00007ffc2d8b62ef R14: 00007f770ba18400 R15: 0000000000022000 > </TASK> I think I figured out the problem. The reproducer actually triggered the below race in madvise_collapse(): CPU A CPU B mmap 0x20000000 - 0x21000000 as anon madvise_collapse is called on this area Retrieve start and end address from the vma (NEVER updated later!) Collapsed the first 2M area and dropped mmap_lock Acquire mmap_lock mmap io_uring file at 0x20563000 Release mmap_lock Reacquire mmap_lock revalidate vma pass since 0x20200000 + 0x200000 > 0x20563000 scan the next 2M (0x20200000 - 0x20400000), but due to whatever reason it didn't release mmap_lock scan the 3rd 2M area (start from 0x20400000) actually scan the new vma created by io_uring since the end was never updated The below patch should be able to fix the problem (untested): diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 5f7c60b8b269..e708c5d62325 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2441,8 +2441,10 @@ int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev, memset(cc->node_load, 0, sizeof(cc->node_load)); result = hpage_collapse_scan_pmd(mm, vma, addr, &mmap_locked, cc); - if (!mmap_locked) + if (!mmap_locked) { *prev = NULL; /* Tell caller we dropped mmap_lock */ + hend = vma->end & HPAGE_PMD_MASK; + } switch (result) { case SCAN_SUCCEED: > >
