* Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> [220427 13:20]: > On Wed, 27 Apr 2022 06:15:20 -0700 syzbot <syzbot+7728e4ab5371cebc9c00@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > syzbot has found a reproducer for the following issue on: > > Thanks. > > userfaultfd_release() appears to have offended vma_merge(). Potentially apply_mlockall_flags() and not userfaultfd_release(). There is a potential that the vma iterator is stale if a split/merge succeeds, although KASAN should pick this up and KASAN is active according to the config below. I've sent a patch for the mlockall issue after Qian Cai's reported it to linux-mm. > > I'm not seeing any changes in that area from Peter, but Liam's > mapletree work changed things around a bit. Gents, could you please > take a look? > > > > HEAD commit: f02ac5c95dfd Add linux-next specific files for 20220427 > > git tree: linux-next > > console output: https://syzkaller.appspot.com/x/log.txt?x=105a33a2f00000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=e9256c70f586da8a > > dashboard link: https://syzkaller.appspot.com/bug?extid=7728e4ab5371cebc9c00 > > 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=15f76f82f00000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12b42c3cf00000 > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+7728e4ab5371cebc9c00@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > ------------[ cut here ]------------ > > WARNING: CPU: 0 PID: 3593 at mm/mmap.c:1072 vma_merge+0x428/0x950 mm/mmap.c:1072 > > I assume this is > > VM_WARN_ON(area && end > area->vm_end); > > But lines change around a lot. It would be great if the script which > generates these reports could quote the code around the indicated file > and line. Like: > > next = find_vma(mm, prev ? prev->vm_end : 0); > area = next; > if (area && area->vm_end == end) /* cases 6, 7, 8 */ > next = find_vma(mm, next->vm_end); > > /* verify some invariant that must be enforced by the caller */ > VM_WARN_ON(prev && addr <= prev->vm_start); > --> VM_WARN_ON(area && end > area->vm_end); > VM_WARN_ON(addr >= end); > > /* > * Can it merge with the predecessor? > */ > if (prev && prev->vm_end == addr && That is the correct line according to the git tree and HEAD commit listed above. I cannot get this issue to trigger with the given tree and git repo with my config. I will try again with the kernel config above. Thanks, Liam
