From: Ingo Molnar <mingo@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: aryabinin@virtuozzo.com, krinkin.m.u@gmail.com, mingo@elte.hu,
peterz@infradead.org, linux-kernel@vger.kernel.org,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: + kernel-locking-lockdepc-make-lockdep-initialize-itself-on-demand.patch added to -mm tree
Date: Tue, 9 Feb 2016 12:12:29 +0100 [thread overview]
Message-ID: <20160209111228.GA32615@gmail.com> (raw)
In-Reply-To: <20160203085111.fc3f2631.akpm@linux-foundation.org>
* Andrew Morton <akpm@linux-foundation.org> wrote:
> > and it should happen in a well defined place, not be opportunistic (and
> > relatively random) like this, making it dependent on config options and
> > calling contexts.
>
> That's an unusable assertion, sorry.
>
> Initializing lockdep in the above manner guarantees that it is initialized
> before it is used. It is *much* more reliable than "try to initialize it before
> some piece of code which hasn't even been written yet tries to take a lock".
So I didn't like that patch because it called into lockdep in a messy way, without
having any real knowledge about whether it's safe to do. Should lockdep ever grow
more complex initialization, such a solution could break in subtle ways. I prefer
clearly broken code with static dependencies over context-dependent broken code
with dynamic call ordering/dependencies.
Fortunately we don't have to apply the patch:
> The conceptual problem is that if some piece of code does spin_lock_init() or
> DEFINE_SPINLOCK(), that lock isn't necessarily initialized yet.
The conceptual problem is that the data structures are not build time initialized
- but the hlist conversion patch solves that problem nicely!
So I'm a happy camper.
Thanks,
Ingo
next prev parent reply other threads:[~2016-02-09 11:12 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <56b11d2d.vVw1kB2la7Y+70xF%akpm@linux-foundation.org>
2016-02-03 7:44 ` + kernel-locking-lockdepc-make-lockdep-initialize-itself-on-demand.patch added to -mm tree Ingo Molnar
2016-02-03 9:42 ` Andrey Ryabinin
2016-02-03 9:49 ` Ingo Molnar
2016-02-03 16:51 ` Andrew Morton
2016-02-03 20:40 ` Andrew Morton
2016-02-03 21:44 ` Andrew Morton
2016-02-04 13:13 ` Andrey Ryabinin
2016-02-08 9:33 ` Michael Ellerman
2016-02-09 11:00 ` Ingo Molnar
2016-02-09 11:12 ` Ingo Molnar [this message]
2016-02-09 20:17 ` Andrew Morton
2016-02-29 9:11 ` Ingo Molnar
2016-02-29 9:25 ` Ingo Molnar
2016-02-29 9:30 ` Andrey Ryabinin
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