linux-kernel - Re: Locking API testsuite: mixed read-lock/lock-write ABBA: |FAILED|

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Date:   Wed, 11 Oct 2017 20:50:14 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jakub Kicinski <kubakici@...pl>
Cc:     LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>
Subject: Re: Locking API testsuite: mixed read-lock/lock-write ABBA: |FAILED|

On Wed, Oct 11, 2017 at 11:28:25AM -0700, Jakub Kicinski wrote:
> I'm seeing a failure on net-next kernels (rc4):
> 
> [    0.000000]   --------------------------------------------------------------------------
> [    0.000000]               recursive read-lock:             |  ok  |             |  ok  |
> [    0.000000]            recursive read-lock #2:             |  ok  |             |  ok  |
> [    0.000000]             mixed read-write-lock:             |  ok  |             |  ok  |
> [    0.000000]             mixed write-read-lock:             |  ok  |             |  ok  |
> [    0.000000]   mixed read-lock/lock-write ABBA:             |FAILED|             |  ok  |
> [    0.000000]    mixed read-lock/lock-read ABBA:             |  ok  |             |  ok  |
> [    0.000000]  mixed write-lock/lock-write ABBA:             |  ok  |             |  ok  |
> [    0.000000]   --------------------------------------------------------------------------
> 
> Is this OK?


Yes,

commit e91498589746065e3ae95d9a00b068e525eec34f
Author: Peter Zijlstra <peterz@...radead.org>
Date:   Wed Aug 23 13:13:11 2017 +0200

    locking/lockdep/selftests: Add mixed read-write ABBA tests
    
    Currently lockdep has limited support for recursive readers, add a few
    mixed read-write ABBA selftests to show the extend of these
    limitations.
    
      [    0.000000] ----------------------------------------------------------------------------
      [    0.000000]                                  | spin |wlock |rlock |mutex | wsem | rsem |
      [    0.000000]   --------------------------------------------------------------------------
    
      [    0.000000]   mixed read-lock/lock-write ABBA:             |FAILED|             |  ok  |
      [    0.000000]    mixed read-lock/lock-read ABBA:             |  ok  |             |  ok  |
      [    0.000000]  mixed write-lock/lock-write ABBA:             |  ok  |             |  ok  |
    
    This clearly illustrates the case where lockdep fails to find a
    deadlock.
    
    Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
    Cc: Linus Torvalds <torvalds@...ux-foundation.org>
    Cc: Peter Zijlstra <peterz@...radead.org>
    Cc: Thomas Gleixner <tglx@...utronix.de>
    Cc: boqun.feng@...il.com
    Cc: byungchul.park@....com
    Cc: david@...morbit.com
    Cc: johannes@...solutions.net
    Cc: oleg@...hat.com
    Cc: tj@...nel.org
    Signed-off-by: Ingo Molnar <mingo@...nel.org>