linux-kernel - Re: [RFC] simple_lmk: Introduce Simple Low Memory Killer for Android

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Message-ID: <20190515145831.GD18892@redhat.com>
Date:   Wed, 15 May 2019 16:58:32 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Sultan Alsawaf <sultan@...neltoast.com>
Cc:     Christian Brauner <christian@...uner.io>,
        Daniel Colascione <dancol@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tim Murray <timmurray@...gle.com>,
        Michal Hocko <mhocko@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:ANDROID DRIVERS" <devel@...verdev.osuosl.org>,
        linux-mm <linux-mm@...ck.org>,
        kernel-team <kernel-team@...roid.com>,
        Andy Lutomirski <luto@...capital.net>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Kees Cook <keescook@...omium.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [RFC] simple_lmk: Introduce Simple Low Memory Killer for Android

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.