Re: possible deadlock in __might_fault (3)

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    a880148cb2af Add linux-next specific files for 20180831
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=16b6013e400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a059d319ef7d83f6
dashboard link: https://syzkaller.appspot.com/bug?extid=6884a790570df1022b2d
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10ecaa46400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17f60151400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+6884a790570df1022b2d@xxxxxxxxxxxxxxxxxxxxxxxxx


======================================================
WARNING: possible circular locking dependency detected
4.19.0-rc1-next-20180831+ #53 Not tainted
------------------------------------------------------
syz-executor560/5342 is trying to acquire lock:
00000000d0c295b6 (&mm->mmap_sem){++++}, at: __might_fault+0xfb/0x1e0  
mm/memory.c:4577

but task is already holding lock:
000000000e449f78 (&rp->fetch_lock){+.+.}, at: mon_bin_get_event+0x3f/0x460  
drivers/usb/mon/mon_bin.c:747

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&rp->fetch_lock){+.+.}:
       __mutex_lock_common kernel/locking/mutex.c:925 [inline]
       __mutex_lock+0x171/0x1700 kernel/locking/mutex.c:1073
       mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1088
       mon_bin_vma_fault+0xdc/0x4a0 drivers/usb/mon/mon_bin.c:1237
       __do_fault+0xee/0x450 mm/memory.c:3240
       do_cow_fault mm/memory.c:3681 [inline]
       do_fault mm/memory.c:3754 [inline]
       handle_pte_fault mm/memory.c:3983 [inline]
       __handle_mm_fault+0x13c6/0x4350 mm/memory.c:4107
       handle_mm_fault+0x53e/0xc80 mm/memory.c:4144
       faultin_page mm/gup.c:518 [inline]
       __get_user_pages+0x823/0x1b50 mm/gup.c:718
       populate_vma_page_range+0x2db/0x3d0 mm/gup.c:1222
       __mm_populate+0x286/0x4d0 mm/gup.c:1270
       mm_populate include/linux/mm.h:2307 [inline]
       vm_mmap_pgoff+0x27f/0x2c0 mm/util.c:362
       ksys_mmap_pgoff+0x4da/0x660 mm/mmap.c:1585
       __do_sys_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
       __se_sys_mmap arch/x86/kernel/sys_x86_64.c:91 [inline]
       __x64_sys_mmap+0xe9/0x1b0 arch/x86/kernel/sys_x86_64.c:91
       do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (&mm->mmap_sem){++++}:
       lock_acquire+0x1e4/0x4f0 kernel/locking/lockdep.c:3901
       __might_fault+0x155/0x1e0 mm/memory.c:4578
       _copy_to_user+0x30/0x110 lib/usercopy.c:25
       copy_to_user include/linux/uaccess.h:155 [inline]
       mon_bin_get_event+0x116/0x460 drivers/usb/mon/mon_bin.c:756
       mon_bin_ioctl+0x459/0xe80 drivers/usb/mon/mon_bin.c:1068
       vfs_ioctl fs/ioctl.c:46 [inline]
       file_ioctl fs/ioctl.c:501 [inline]
       do_vfs_ioctl+0x1de/0x1720 fs/ioctl.c:685
       ksys_ioctl+0xa9/0xd0 fs/ioctl.c:702
       __do_sys_ioctl fs/ioctl.c:709 [inline]
       __se_sys_ioctl fs/ioctl.c:707 [inline]
       __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:707
       do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&rp->fetch_lock);
                               lock(&mm->mmap_sem);
                               lock(&rp->fetch_lock);
  lock(&mm->mmap_sem);

 *** DEADLOCK ***

1 lock held by syz-executor560/5342:
 #0: 000000000e449f78 (&rp->fetch_lock){+.+.}, at:  
mon_bin_get_event+0x3f/0x460 drivers/usb/mon/mon_bin.c:747

stack backtrace:
CPU: 0 PID: 5342 Comm: syz-executor560 Not tainted  
4.19.0-rc1-next-20180831+ #53
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1c9/0x2b4 lib/dump_stack.c:113
 print_circular_bug.isra.34.cold.55+0x1bd/0x27d  
kernel/locking/lockdep.c:1222
 check_prev_add kernel/locking/lockdep.c:1862 [inline]
 check_prevs_add kernel/locking/lockdep.c:1975 [inline]
 validate_chain kernel/locking/lockdep.c:2416 [inline]
 __lock_acquire+0x3449/0x5020 kernel/locking/lockdep.c:3412
 lock_acquire+0x1e4/0x4f0 kernel/locking/lockdep.c:3901
 __might_fault+0x155/0x1e0 mm/memory.c:4578
 _copy_to_user+0x30/0x110 lib/usercopy.c:25
 copy_to_user include/linux/uaccess.h:155 [inline]
 mon_bin_get_event+0x116/0x460 drivers/usb/mon/mon_bin.c:756
 mon_bin_ioctl+0x459/0xe80 drivers/usb/mon/mon_bin.c:1068
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:501 [inline]
 do_vfs_ioctl+0x1de/0x1720 fs/ioctl.c:685
 ksys_ioctl+0xa9/0xd0 fs/ioctl.c:702
 __do_sys_ioctl fs/ioctl.c:709 [inline]
 __se_sys_ioctl fs/ioctl.c:707 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:707
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x44a139
Code: e8 6c b4 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 4b cd fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fa6f2498da8 EFLAGS: 00000293 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006dbc68 RCX: 000000000044a139
RDX: 0000000020000000 RSI: 000000004018920a RDI: 0000000000000005
RBP: 00000000006dbc60 R08: 00007fa6f2499700 R09: 0000000000000000
R10: 00007fa6f2499700 R11: 0000000000000293 R12: 00000000006dbc6c
R13: 6273752f7665642f R14: 7375622f7665642f R15: 00000000006dbd4c