Re: [load_elf_binary] WARNING: bad unlock balance detected!

[Fengguang Wu]

Sorry please ignore this report -- according to Peter:

This is fixed by commit:

 02a7c234e540 ("rcu: Suppress lockdep false-positive ->boost_mtx complaints")

The problem is that RCU boosting was mixing futex and !futex rt_mutex
ops.

On Tue, Nov 07, 2017 at 09:55:56AM +0800, Fengguang Wu wrote:
> Hi,
>
> Here is a warning in v4.14-rc8 -- it's not necessarily a new bug.
>
> [   66.941105] 8021q: adding VLAN 0 to HW filter on device eth0
> [   67.243706] 8021q: adding VLAN 0 to HW filter on device eth0
> LKP: HOSTNAME vm-lkp-nex04-openwrt-ia32-4, MAC , kernel 4.14.0-rc8 158, serial console /dev/ttyS0
> [   67.943691]
> [   67.944258] =====================================
> [   67.945424] WARNING: bad unlock balance detected!
> [   67.946566] 4.14.0-rc8 #158 Not tainted
> [   67.947527] -------------------------------------
> [   67.948461] grep/1361 is trying to release lock (rcu_preempt_state) at:
> [   67.949772] [<c10e4348>] rcu_read_unlock_special+0x5f8/0x620
> [   67.950843] but there are no more locks to release!
> [   67.951839]
> [   67.951839] other info that might help us debug this:
> [   67.953115] 2 locks held by grep/1361:
> [   67.953881]  #0:  (&mm->mmap_sem){....}, at: [<c105194e>] __do_page_fault+0x2de/0xb40
> [   67.955392]  #1:  (rcu_read_lock){....}, at: [<c11a5900>] find_get_entry+0x0/0x420
> [   67.956841]
> [   67.956841] stack backtrace:
> [   67.957765] CPU: 0 PID: 1361 Comm: grep Not tainted 4.14.0-rc8 #158
> [   67.958944] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> [   67.960553] Call Trace:
> [   67.962208]  dump_stack+0x16/0x1c
> [   67.962949]  print_unlock_imbalance_bug+0xb9/0xd0
> [   67.963871]  ? rcu_read_unlock_special+0x5f8/0x620
> [   67.964908]  ? rcu_read_unlock_special+0x5f8/0x620
> [   67.965847]  lock_release+0x1cc/0x490
> [   67.966599]  ? rcu_read_unlock_special+0x5f8/0x620
> [   67.967551]  ? _raw_spin_unlock_irqrestore+0x86/0xd0
> [   67.968543]  rt_mutex_unlock+0x1e/0xb0
> [   67.969312]  rcu_read_unlock_special+0x5f8/0x620
> [   67.970280]  __rcu_read_unlock+0xa7/0xb0
> [   67.971067]  find_get_entry+0x2ef/0x420
> [   67.971856]  pagecache_get_page+0x1c/0x650
> [   67.972684]  filemap_fault+0x105/0xd90
> [   67.973468]  __do_fault+0x17/0x1d0
> [   67.974176]  handle_mm_fault+0x1360/0x1d30
> [   67.974994]  __do_page_fault+0x5a3/0xb40
> [   67.975798]  ? kvm_read_and_reset_pf_reason+0x40/0x40
> [   67.976777]  do_page_fault+0x30/0x250
> [   67.977529]  ? kvm_read_and_reset_pf_reason+0x40/0x40
> [   67.978500]  do_async_page_fault+0x2e/0xa0
> [   67.979321]  common_exception+0x65/0x6a
> [   67.980156] EIP: clear_user+0x128/0x170
> [   67.980927] EFLAGS: 00010246 CPU: 0
> [   67.981652] EAX: 00000000 EBX: 000003fe ECX: 000003fe EDX: 00000003
> [   67.982821] ESI: b7fc0000 EDI: b7fbf005 EBP: ddda7e94 ESP: ddda7e80
> [   67.984010]  DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068
> [   67.985058]  ? handle_mm_fault+0x700/0x1d30
> [   67.985902]  ? kvm_read_and_reset_pf_reason+0x40/0x40
> [   67.986881]  padzero+0x3c/0x60
> [   67.987548]  load_elf_binary+0x1908/0x1bf0
> [   67.988370]  ? _raw_read_unlock+0x55/0x90
> [   67.989180]  search_binary_handler+0xd9/0x160
> [   67.990102]  do_execveat_common+0x8f3/0xb10
> [   67.990960]  SyS_execve+0x1f/0x30
> [   67.991673]  do_int80_syscall_32+0x95/0x290
> [   67.992508]  entry_INT80_32+0x2f/0x2f
> [   67.993266] EIP: 0xb7f38b07
> [   67.993866] EFLAGS: 00000296 CPU: 0
> [   67.994627] EAX: ffffffda EBX: 08097394 ECX: 0809728c EDX: 080972a4
> [   67.995831] ESI: 08097394 EDI: 080972a4 EBP: bfbeb778 ESP: bfbeb754
> [   67.996998]  DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 007b
> [   68.012659] grep (1361) used greatest stack depth: 6232 bytes left
> [   69.303817] e1000: eth0 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX
>
> Thanks,
> Fengguang