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 > > > 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?
