linux-kernel - Re: [load_elf_binary] WARNING: bad unlock balance detected!

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Date:   Tue, 7 Nov 2017 20:29:42 +0800
From:   Fengguang Wu <fengguang.wu@...el.com>
To:     linux-fsdevel@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        David Howells <dhowells@...hat.com>,
        Roland McGrath <roland@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [load_elf_binary] WARNING: bad unlock balance detected!

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