Re: [syzbot] possible deadlock in hugetlb_fault

[Mike Kravetz <mike.kravetz@oracle.com>]

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@syzkaller.appspotmail.com
> 
> ======================================================
> 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?
-- 
Mike Kravetz

> 
> 
> 1 lock held by syz-executor.2/5665:
>  #0: ffff88801c4f3078 (&vma_lock->rw_sema){++++}-{3:3}, at: hugetlb_vma_lock_read mm/hugetlb.c:6816 [inline]
>  #0: ffff88801c4f3078 (&vma_lock->rw_sema){++++}-{3:3}, at: hugetlb_fault+0x40a/0x2060 mm/hugetlb.c:5859
> 
> stack backtrace:
> CPU: 1 PID: 5665 Comm: syz-executor.2 Not tainted 6.1.0-rc3-syzkaller-00152-gf2f32f8af2b0 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/11/2022
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
>  check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2177
>  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
> RIP: 0023:0xf7fad549
> Code: 03 74 c0 01 10 05 03 74 b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d b4 26 00 00 00 00 8d b4 26 00 00 00 00
> RSP: 002b:00000000f7f875cc EFLAGS: 00000296 ORIG_RAX: 0000000000000004
> RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 0000000020000000
> RDX: 00000000c86ade39 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>  </TASK>
> ----------------
> Code disassembly (best guess):
>    0:	03 74 c0 01          	add    0x1(%rax,%rax,8),%esi
>    4:	10 05 03 74 b8 01    	adc    %al,0x1b87403(%rip)        # 0x1b8740d
>    a:	10 06                	adc    %al,(%rsi)
>    c:	03 74 b4 01          	add    0x1(%rsp,%rsi,4),%esi
>   10:	10 07                	adc    %al,(%rdi)
>   12:	03 74 b0 01          	add    0x1(%rax,%rsi,4),%esi
>   16:	10 08                	adc    %cl,(%rax)
>   18:	03 74 d8 01          	add    0x1(%rax,%rbx,8),%esi
>   1c:	00 00                	add    %al,(%rax)
>   1e:	00 00                	add    %al,(%rax)
>   20:	00 51 52             	add    %dl,0x52(%rcx)
>   23:	55                   	push   %rbp
>   24:	89 e5                	mov    %esp,%ebp
>   26:	0f 34                	sysenter
>   28:	cd 80                	int    $0x80
> * 2a:	5d                   	pop    %rbp <-- trapping instruction
>   2b:	5a                   	pop    %rdx
>   2c:	59                   	pop    %rcx
>   2d:	c3                   	retq
>   2e:	90                   	nop
>   2f:	90                   	nop
>   30:	90                   	nop
>   31:	90                   	nop
>   32:	8d b4 26 00 00 00 00 	lea    0x0(%rsi,%riz,1),%esi
>   39:	8d b4 26 00 00 00 00 	lea    0x0(%rsi,%riz,1),%esi
> 
> 
> ---
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