On Mon, Sep 12, 2022 at 2:47 PM Yang Shi <shy828301@xxxxxxxxx> wrote: > > 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; > + } This is wrong. We should refetch the vma end after hugepage_vma_revalidate() otherwise the vma is still the old one. diff --git a/mm/khugepaged.c b/mm/khugepaged.c index a3acd3e5e0f3..1860be232a26 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2592,6 +2592,8 @@ int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev, last_fail = result; goto out_nolock; } + + hend = vma->vm_end & HPAGE_PMD_MASK; } mmap_assert_locked(mm); memset(cc->node_load, 0, sizeof(cc->node_load)); > > switch (result) { > case SCAN_SUCCEED: > > > > > >
