On Mon, 14 Nov 2022 at 03:35, 'Miaohe Lin' via syzkaller-bugs <syzkaller-bugs@xxxxxxxxxxxxxxxx> wrote: > > On 2022/11/12 22:14, Dmitry Vyukov wrote: > > On Sat, 12 Nov 2022 at 12:33, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > >> > >> On Sat, 12 Nov 2022 at 05:02, 'Miaohe Lin' via syzkaller-bugs > >> <syzkaller-bugs@xxxxxxxxxxxxxxxx> wrote: > >>> > >>> On 2022/11/12 8:07, Mike Kravetz wrote: > >>>> On 11/04/22 09:00, syzbot wrote: > >>>>> Hello, > >>>>> > >>>>> syzbot found the following issue on: > >>>>> > >>>>> HEAD commit: f2f32f8af2b0 Merge tag 'for-6.1-rc3-tag' of git://git.kern.. > >>>>> git tree: upstream > >>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=137d52ca880000 > >>>>> kernel config: https://syzkaller.appspot.com/x/.config?x=d080a4bd239918dd > >>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=ca56f14c500045350f93 > >>>>> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 > >>>>> userspace arch: i386 > >>>>> > >>>>> Unfortunately, I don't have any reproducer for this issue yet. > >>>>> > >>>>> Downloadable assets: > >>>>> disk image: https://storage.googleapis.com/syzbot-assets/b4f72e7a4c11/disk-f2f32f8a.raw.xz > >>>>> vmlinux: https://storage.googleapis.com/syzbot-assets/3f88997ad7c9/vmlinux-f2f32f8a.xz > >>>>> kernel image: https://storage.googleapis.com/syzbot-assets/b4b5b3963e2d/bzImage-f2f32f8a.xz > >>>>> > >>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit: > >>>>> Reported-by: syzbot+ca56f14c500045350f93@xxxxxxxxxxxxxxxxxxxxxxxxx > >>>>> > >>>>> ====================================================== > >>>>> WARNING: possible circular locking dependency detected > >>>>> 6.1.0-rc3-syzkaller-00152-gf2f32f8af2b0 #0 Not tainted > >>>>> ------------------------------------------------------ > >>>>> syz-executor.2/5665 is trying to acquire lock: > >>>>> ffff88801c74c298 (&mm->mmap_lock#2){++++}-{3:3}, at: __might_fault+0xa1/0x170 mm/memory.c:5645 > >>>>> > >>>>> but task is already holding lock: > >>>>> ffff88801c4f3078 (&vma_lock->rw_sema){++++}-{3:3}, at: hugetlb_vma_lock_read mm/hugetlb.c:6816 [inline] > >>>>> ffff88801c4f3078 (&vma_lock->rw_sema){++++}-{3:3}, at: hugetlb_fault+0x40a/0x2060 mm/hugetlb.c:5859 > >>>>> > >>>>> which lock already depends on the new lock. > >>>>> > >>>>> > >>>>> the existing dependency chain (in reverse order) is: > >>>>> > >>>>> -> #1 (&vma_lock->rw_sema){++++}-{3:3}: > >>>>> down_write+0x90/0x220 kernel/locking/rwsem.c:1562 > >>>>> hugetlb_vma_lock_write mm/hugetlb.c:6834 [inline] > >>>>> __unmap_hugepage_range_final+0x97/0x340 mm/hugetlb.c:5202 > >>>>> unmap_single_vma+0x23d/0x2a0 mm/memory.c:1690 > >>>>> unmap_vmas+0x21e/0x370 mm/memory.c:1733 > >>>>> exit_mmap+0x189/0x7a0 mm/mmap.c:3090 > >>>>> __mmput+0x128/0x4c0 kernel/fork.c:1185 > >>>>> mmput+0x5c/0x70 kernel/fork.c:1207 > >>>>> exit_mm kernel/exit.c:516 [inline] > >>>>> do_exit+0xa39/0x2a20 kernel/exit.c:807 > >>>>> do_group_exit+0xd0/0x2a0 kernel/exit.c:950 > >>>>> get_signal+0x21a1/0x2430 kernel/signal.c:2858 > >>>>> arch_do_signal_or_restart+0x82/0x2300 arch/x86/kernel/signal.c:869 > >>>>> exit_to_user_mode_loop kernel/entry/common.c:168 [inline] > >>>>> exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203 > >>>>> __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline] > >>>>> syscall_exit_to_user_mode+0x19/0x50 kernel/entry/common.c:296 > >>>>> __do_fast_syscall_32+0x72/0xf0 arch/x86/entry/common.c:181 > >>>>> do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:203 > >>>>> entry_SYSENTER_compat_after_hwframe+0x70/0x82 > >>>>> > >>>>> -> #0 (&mm->mmap_lock#2){++++}-{3:3}: > >>>>> check_prev_add kernel/locking/lockdep.c:3097 [inline] > >>>>> check_prevs_add kernel/locking/lockdep.c:3216 [inline] > >>>>> validate_chain kernel/locking/lockdep.c:3831 [inline] > >>>>> __lock_acquire+0x2a43/0x56d0 kernel/locking/lockdep.c:5055 > >>>>> lock_acquire kernel/locking/lockdep.c:5668 [inline] > >>>>> lock_acquire+0x1df/0x630 kernel/locking/lockdep.c:5633 > >>>>> __might_fault mm/memory.c:5646 [inline] > >>>>> __might_fault+0x104/0x170 mm/memory.c:5639 > >>>>> _copy_from_user+0x25/0x170 lib/usercopy.c:13 > >>>>> copy_from_user include/linux/uaccess.h:161 [inline] > >>>>> snd_rawmidi_kernel_write1+0x366/0x880 sound/core/rawmidi.c:1549 > >>>>> snd_rawmidi_write+0x273/0xbb0 sound/core/rawmidi.c:1618 > >>>>> vfs_write+0x2d7/0xdd0 fs/read_write.c:582 > >>>>> ksys_write+0x1e8/0x250 fs/read_write.c:637 > >>>>> do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline] > >>>>> __do_fast_syscall_32+0x65/0xf0 arch/x86/entry/common.c:178 > >>>>> do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:203 > >>>>> entry_SYSENTER_compat_after_hwframe+0x70/0x82 > >>>>> > >>>>> other info that might help us debug this: > >>>>> > >>>>> Possible unsafe locking scenario: > >>>>> > >>>>> CPU0 CPU1 > >>>>> ---- ---- > >>>>> lock(&vma_lock->rw_sema); > >>>>> lock(&mm->mmap_lock#2); > >>>>> lock(&vma_lock->rw_sema); > >>>>> lock(&mm->mmap_lock#2); > >>>> > >>>> I may not be reading the report correctly, but I can not see how we acquire the > >>>> hugetlb vma_lock before trying to acquire mmap_lock in stack 0. We would not > >>>> acquire the vma_lock until we enter hugetlb fault processing (not in the stack). > >> > >> The unlock of vma_lock is conditional: > >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/hugetlb.c?id=f2f32f8af2b0ca9d619e5183eae3eed431793baf#n6840 > >> > >> and the condition is: > >> > >> static bool __vma_shareable_flags_pmd(struct vm_area_struct *vma) > >> { > >> return vma->vm_flags & (VM_MAYSHARE | VM_SHARED) && > >> vma->vm_private_data; > >> } > >> > >> Is it possible that the condition has changed between vma lock and unlock? > >> What mutexes protect vma->vm_flags/vm_private_data? > >> > >> That would make the report perfectly sensible. > >> > >> FWIW the test case that was running is this, that's the syscalls that > >> were running concurrently: > >> > >> 07:56:56 executing program 2: > >> r0 = syz_open_dev$sndmidi(&(0x7f0000000040), 0x2, 0x141101) > >> r1 = dup(r0) > >> setsockopt$inet_sctp_SCTP_I_WANT_MAPPED_V4_ADDR(r1, 0x84, 0xc, > >> &(0x7f0000000080), 0x4) (async) > >> write$6lowpan_enable(r1, &(0x7f0000000000)='0', 0xc86ade39) (async) > >> mmap(&(0x7f0000000000/0xb36000)=nil, 0xb36000, 0x3, 0x68831, > >> 0xffffffffffffffff, 0x0) (async) > >> madvise(&(0x7f0000000000/0x600000)=nil, 0x600003, 0x4) (async, rerun: 32) > >> mremap(&(0x7f00007a0000/0x3000)=nil, 0x3000, 0x2000, 0x7, > >> &(0x7f0000835000/0x2000)=nil) (rerun: 32) > > > > > > This new bug report seems to confirm the hypothesis: > > > > WARNING: locking bug in hugetlb_no_page > > https://syzkaller.appspot.com/bug?extid=d07c65298d2c15eafcb0 > > Thanks Dmitry! > > I believe Mike found the root cause and his proposed patches in next-20221111 will fix the problem: > https://lore.kernel.org/linux-mm/20221111232628.290160-1-mike.kravetz@xxxxxxxxxx/ > > Let's keep looking. :) Thanks for your work! Let's tell syzbot about the fix so that it reports similar issues in future: #syz fix: hugetlb: don't delete vma_lock in hugetlb MADV_DONTNEED processing > Thanks, > Miaohe Lin > > > > > > > >>>> Adding Miaohe Lin on Cc due to previous help with vma_lock potential deadlock > >>>> situations. Miaohe, does this make sense to you? > >>>> > >>> > >>> Hi Mike, > >>> This doesn't make sense for me too. Stack #1 shows that syz-executor is releasing > >>> its address space while stack #0 shows another thread is serving the write syscall. > >>> In this case, mm->mm_users is 0 and all threads in this process should be serving > >>> do_exit()? But I could be easily wrong. Also I can't see how vma_lock is locked before > >>> trying to acquire mmap_lock in above stacks. Might this be a false positive? > > . > > > > -- > You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group. > To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bugs+unsubscribe@xxxxxxxxxxxxxxxx. > To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/4c5fa6b4-6278-ce2b-73c2-883eb734bdc7%40huawei.com.
