Re: possible deadlock in ovl_write_iter

[syzbot <syzbot+695726bc473f9c36a4b6@syzkaller.appspotmail.com>]

syzbot has found a reproducer for the following crash on:

HEAD commit:    6f8b52ba442c Merge tag 'hwmon-for-v4.20-rc5' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=120f3905400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c94f9f0c0363db4b
dashboard link: https://syzkaller.appspot.com/bug?extid=695726bc473f9c36a4b6
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10cad225400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13813093400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+695726bc473f9c36a4b6@syzkaller.appspotmail.com

overlayfs: filesystem on './file0' not supported as upperdir

======================================================
WARNING: possible circular locking dependency detected
4.20.0-rc4+ #351 Not tainted
------------------------------------------------------
syz-executor338/5996 is trying to acquire lock:
00000000b59bb66d (&ovl_i_mutex_key[depth]){+.+.}, at: inode_lock  
include/linux/fs.h:757 [inline]
00000000b59bb66d (&ovl_i_mutex_key[depth]){+.+.}, at:  
ovl_write_iter+0x151/0xd10 fs/overlayfs/file.c:231

but task is already holding lock:
00000000e0274330 (&pipe->mutex/1){+.+.}, at: pipe_lock_nested fs/pipe.c:62  
[inline]
00000000e0274330 (&pipe->mutex/1){+.+.}, at: pipe_lock+0x6e/0x80  
fs/pipe.c:70

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&pipe->mutex/1){+.+.}:
        __mutex_lock_common kernel/locking/mutex.c:925 [inline]
        __mutex_lock+0x166/0x16f0 kernel/locking/mutex.c:1072
        mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
        pipe_lock_nested fs/pipe.c:62 [inline]
        pipe_lock+0x6e/0x80 fs/pipe.c:70
        iter_file_splice_write+0x27d/0x1050 fs/splice.c:700
        do_splice_from fs/splice.c:851 [inline]
        do_splice+0x64a/0x1430 fs/splice.c:1147
        __do_sys_splice fs/splice.c:1414 [inline]
        __se_sys_splice fs/splice.c:1394 [inline]
        __x64_sys_splice+0x2c1/0x330 fs/splice.c:1394
        do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
        entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #1 (sb_writers#3){.+.+}:
        percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:36  
[inline]
        percpu_down_read include/linux/percpu-rwsem.h:59 [inline]
        __sb_start_write+0x214/0x370 fs/super.c:1387
        sb_start_write include/linux/fs.h:1597 [inline]
        mnt_want_write+0x3f/0xc0 fs/namespace.c:360
        ovl_want_write+0x76/0xa0 fs/overlayfs/util.c:24
        ovl_setattr+0x10b/0xaf0 fs/overlayfs/inode.c:30
        notify_change+0xbde/0x1110 fs/attr.c:334
        do_truncate+0x1bd/0x2d0 fs/open.c:63
        handle_truncate fs/namei.c:3008 [inline]
        do_last fs/namei.c:3424 [inline]
        path_openat+0x375f/0x5150 fs/namei.c:3534
        do_filp_open+0x255/0x380 fs/namei.c:3564
        do_sys_open+0x568/0x700 fs/open.c:1063
        __do_sys_openat fs/open.c:1090 [inline]
        __se_sys_openat fs/open.c:1084 [inline]
        __x64_sys_openat+0x9d/0x100 fs/open.c:1084
        do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
        entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (&ovl_i_mutex_key[depth]){+.+.}:
        lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3844
        down_write+0x8a/0x130 kernel/locking/rwsem.c:70
        inode_lock include/linux/fs.h:757 [inline]
        ovl_write_iter+0x151/0xd10 fs/overlayfs/file.c:231
        call_write_iter include/linux/fs.h:1857 [inline]
        new_sync_write fs/read_write.c:474 [inline]
        __vfs_write+0x6b8/0x9f0 fs/read_write.c:487
        __kernel_write+0x10c/0x370 fs/read_write.c:506
        write_pipe_buf+0x180/0x240 fs/splice.c:797
        splice_from_pipe_feed fs/splice.c:503 [inline]
        __splice_from_pipe+0x38b/0x7c0 fs/splice.c:627
        splice_from_pipe+0x1ec/0x340 fs/splice.c:662
        default_file_splice_write+0x3c/0x90 fs/splice.c:809
        do_splice_from fs/splice.c:851 [inline]
        do_splice+0x64a/0x1430 fs/splice.c:1147
        __do_sys_splice fs/splice.c:1414 [inline]
        __se_sys_splice fs/splice.c:1394 [inline]
        __x64_sys_splice+0x2c1/0x330 fs/splice.c:1394
        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:

Chain exists of:
   &ovl_i_mutex_key[depth] --> sb_writers#3 --> &pipe->mutex/1

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(&pipe->mutex/1);
                                lock(sb_writers#3);
                                lock(&pipe->mutex/1);
   lock(&ovl_i_mutex_key[depth]);

  *** DEADLOCK ***

2 locks held by syz-executor338/5996:
  #0: 00000000024e7b73 (sb_writers#8){.+.+}, at: file_start_write  
include/linux/fs.h:2810 [inline]
  #0: 00000000024e7b73 (sb_writers#8){.+.+}, at: do_splice+0xd2e/0x1430  
fs/splice.c:1146
  #1: 00000000e0274330 (&pipe->mutex/1){+.+.}, at: pipe_lock_nested  
fs/pipe.c:62 [inline]
  #1: 00000000e0274330 (&pipe->mutex/1){+.+.}, at: pipe_lock+0x6e/0x80  
fs/pipe.c:70

stack backtrace:
CPU: 0 PID: 5996 Comm: syz-executor338 Not tainted 4.20.0-rc4+ #351
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+0x244/0x39d lib/dump_stack.c:113
  print_circular_bug.isra.35.cold.54+0x1bd/0x27d  
kernel/locking/lockdep.c:1221
  check_prev_add kernel/locking/lockdep.c:1863 [inline]
  check_prevs_add kernel/locking/lockdep.c:1976 [inline]
  validate_chain kernel/locking/lockdep.c:2347 [inline]
  __lock_acquire+0x3399/0x4c20 kernel/locking/lockdep.c:3341
  lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3844
  down_write+0x8a/0x130 kernel/locking/rwsem.c:70
  inode_lock include/linux/fs.h:757 [inline]
  ovl_write_iter+0x151/0xd10 fs/overlayfs/file.c:231
  call_write_iter include/linux/fs.h:1857 [inline]
  new_sync_write fs/read_write.c:474 [inline]
  __vfs_write+0x6b8/0x9f0 fs/read_write.c:487
  __kernel_write+0x10c/0x370 fs/read_write.c:506
  write_pipe_buf+0x180/0x240 fs/splice.c:797
  splice_from_pipe_feed fs/splice.c:503 [inline]
  __splice_from_pipe+0x38b/0x7c0 fs/splice.c:627
  splice_from_pipe+0x1ec/0x340 fs/splice.c:662
  default_file_splice_write+0x3c/0x90 fs/splice.c:809
  do_splice_from fs/splice.c:851 [inline]
  do_splice+0x64a/0x1430 fs/splice.c:1147
  __do_sys_splice fs/splice.c:1414 [inline]
  __se_sys_splice fs/splice.c:1394 [inline]
  __x64_sys_splice+0x2c1/0x330 fs/splice.c:1394
  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x445ad9
Code: e8 5c b7 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 2b 12 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f18e3f71cd8 EFLAGS: 00000216 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00000000006dac78 RCX: 0000000000445ad9
RDX: 000000000000000a RSI: 0000000000000000 RDI: 0000000000000007
RBP: 00000000006dac70 R08: 000100000000000a R09: 0000000000000007
R10: 0000000000000000 R11: 0000000000000216 R12: 00000000006dac7c
R13: 00007ffde0706e9f R14: 00007f18e3f729c0 R15: 00000000006dad4c