duplicate lock v 5.2-release

[Radim Kolar]

acquiring duplicate lock of same type: "vnode interlock"
 1st vnode interlock @ ufs/ffs/ffs_snapshot.c:488
  2nd vnode interlock @ ufs/ffs/ffs_snapshot.c:491
  Stack backtrace:
  backtrace(c05ff3e6,c0603a90,c0607521,1eb,246) at backtrace+0x17
  witness_lock(c2f20618,8,c0607521,1eb,c2a05978) at witness_lock+0x672
  _mtx_lock_flags(c2f20618,0,c0607518,1eb,c12b2e80) at _mtx_lock_flags+0xba
  ffs_snapshot(c2a07c00,bfbfee21,70,88e,c0649fe8) at ffs_snapshot+0x1759
  ffs_mount(c2a07c00,c2e42a00,bfbfe888,cef06bec,c2cab140) at ffs_mount+0x638
  vfs_domount(c2cab140,c293e670,c2e42a00,1010000,bfbfe888) at vfs_domount+0x7a8
  mount(c2cab140,cef06d14,c060fa0b,3ee,4) at mount+0xc0
  syscall(2f,2f,2f,bfbfe8f8,bfbfee1b) at syscall+0x2c0
  Xint0x80_syscall() at Xint0x80_syscall+0x1d
  --- syscall (21), eip = 0x280bde1f, esp = 0xbfbfe80c, ebp = 0xbfbfed10 ---
Ma cenu hlasit takoveto chyby jako pr?