linux-kernel - Re: [locking/ww_mutex] 857811a371 BUG: kernel hang in boot stage

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Date:   Fri, 31 Mar 2017 14:46:41 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Fengguang Wu <fengguang.wu@...el.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, LKP <lkp@...org>
Subject: Re: [locking/ww_mutex] 857811a371 BUG: kernel hang in boot stage

On Tue, Mar 28, 2017 at 05:07:09PM +0800, Fengguang Wu wrote:
> Greetings,
> 
> 0day kernel testing robot got the below dmesg and the first bad commit is
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> 
> commit 857811a37129f5d2ba162d7be3986eff44724014
> Author:     Boqun Feng <boqun.feng@...il.com>
> AuthorDate: Wed Mar 1 23:01:38 2017 +0800
> Commit:     Ingo Molnar <mingo@...nel.org>
> CommitDate: Thu Mar 2 09:00:39 2017 +0100
> 
>      locking/ww_mutex: Adjust the lock number for stress test
>      
>      Because there are only 12 bits in held_lock::references, so we only
>      support 4095 nested lock held in the same time, adjust the lock number
>      for ww_mutex stress test to kill one lockdep splat:
>      
>        [ ] [ BUG: bad unlock balance detected! ]
>        [ ] kworker/u2:0/5 is trying to release lock (ww_class_mutex) at:
>        [ ] ww_mutex_unlock()
>        [ ] but there are no more locks to release!
>        ...
>      
>      Signed-off-by: Boqun Feng <boqun.feng@...il.com>
>      Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>      Cc: Andrew Morton <akpm@...ux-foundation.org>
>      Cc: Chris Wilson <chris@...is-wilson.co.uk>
>      Cc: Fengguang Wu <fengguang.wu@...el.com>
>      Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>      Cc: Nicolai Hähnle <Nicolai.Haehnle@....com>
>      Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>      Cc: Peter Zijlstra <peterz@...radead.org>
>      Cc: Thomas Gleixner <tglx@...utronix.de>
>      Link: http://lkml.kernel.org/r/20170301150138.hdixnmafzfsox7nn@tardis.cn.ibm.com
>      Signed-off-by: Ingo Molnar <mingo@...nel.org>
> 
> 7fb4a2cea6  locking/lockdep: Add nest_lock integrity test
> 857811a371  locking/ww_mutex: Adjust the lock number for stress test
> c02ed2e75e  Linux 4.11-rc4
> 7f0c4a163a  Add linux-next specific files for 20170327
> +-----------------------------------------------------+------------+------------+-----------+---------------+
> |                                                     | 7fb4a2cea6 | 857811a371 | v4.11-rc4 | next-20170327 |
> +-----------------------------------------------------+------------+------------+-----------+---------------+
> | boot_successes                                      | 0          | 16         | 29        | 1             |
> | boot_failures                                       | 221        | 42         | 64        | 9             |
> | WARNING:at_kernel/locking/lockdep.c:#__lock_acquire | 221        |            |           |               |
> | BUG:kernel_hang_in_boot_stage                       | 0          | 42         | 60        | 9             |
> | BUG:kernel_hang_in_test_stage                       | 0          | 0          | 4         |               |
> +-----------------------------------------------------+------------+------------+-----------+---------------+
> 
> [  319.426004] CPU 0 is now offline
> [  319.426004] CPU 0 is now offline
> [  319.427670] 
> <kernel hangs here>
> 

Hmm.. with the same reproduce script, I'm able to reproduce the hang
even with CONIFG_WW_MUTEX_SELFTEST=N. Fengguang, could you try to verify
whether ww_mutex test is related to this hang?

Regards,
Boqun

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