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Date:   Wed, 15 May 2019 16:58:32 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     Sultan Alsawaf <sultan@kerneltoast.com>
Cc:     Christian Brauner <christian@brauner.io>,
        Daniel Colascione <dancol@google.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Tim Murray <timmurray@google.com>,
        Michal Hocko <mhocko@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Arve =?iso-8859-1?B?SGr4bm5lduVn?= <arve@android.com>,
        Todd Kjos <tkjos@android.com>,
        Martijn Coenen <maco@android.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "open list:ANDROID DRIVERS" <devel@driverdev.osuosl.org>,
        linux-mm <linux-mm@kvack.org>,
        kernel-team <kernel-team@android.com>,
        Andy Lutomirski <luto@amacapital.net>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Kees Cook <keescook@chromium.org>,
        Joel Fernandes <joel@joelfernandes.org>
Subject: Re: [RFC] simple_lmk: Introduce Simple Low Memory Killer for Android
Message-ID: <20190515145831.GD18892@redhat.com>
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On 05/13, Sultan Alsawaf wrote:
>
> On Fri, May 10, 2019 at 05:10:25PM +0200, Oleg Nesterov wrote:
> > I am starting to think I am ;)
> >
> > If you have task1 != task2 this code
> >
> > 	task_lock(task1);
> > 	task_lock(task2);
> >
> > should trigger print_deadlock_bug(), task1->alloc_lock and task2->alloc_lock are
> > the "same" lock from lockdep pov, held_lock's will have the same hlock_class().
>
> Okay, I've stubbed out debug_locks_off(), and lockdep is now complaining about a
> bunch of false positives so it is _really_ enabled this time.

Could you explain in detail what exactly did you do and what do you see in dmesg?

Just in case, lockdep complains only once, print_circular_bug() does debug_locks_off()
so it it has already reported another false positive __lock_acquire() will simply
return after that.

Oleg.