linux-kernel - Re: [PATCH] locking/spinlock_debug: Remove spinlock lockup detection code

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Message-ID: <20170209154617.GE6515@twins.programming.kicks-ass.net>
Date:   Thu, 9 Feb 2017 16:46:17 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] locking/spinlock_debug: Remove spinlock lockup detection
 code

On Wed, Feb 08, 2017 at 02:46:48PM -0500, Waiman Long wrote:
> The current spinlock lockup detection code can sometimes produce false
> positives because of the unfairness of the locking algorithm itself.

Also, __delay(1) can be really terrible, which then causes the timeout
to be highly variable and prone to triggering.

> So the lockup detection code is now removed. Instead, we are relying
> on the NMI watchdog to detect potential lockup. We won't have lockup
> detection if the watchdog isn't running.
> 
> The commented-out read-write lock lockup detection code are also
> removed.

Yes, this retains all the extra validation fields, which I've meanwhile
heard are sometimes useful but does away with all the fragile bits.


Thanks!