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). > > 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? Thanks, Miaohe Lin
