linux-kernel - Re: [PATCH tip/core/rcu 6/7] mm: Replace spin_is

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Date:   Thu, 15 Nov 2018 23:05:00 -0800
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        Lance Roy <ldr709@...il.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Jan Kara <jack@...e.cz>, Shakeel Butt <shakeelb@...gle.com>,
        linux-mm@...ck.org
Subject: Re: [PATCH tip/core/rcu 6/7] mm: Replace spin_is_locked() with
 lockdep

On Thu, Nov 15, 2018 at 10:49:17AM -0800, Davidlohr Bueso wrote:
> On Sun, 11 Nov 2018, Paul E. McKenney wrote:
> 
> >From: Lance Roy <ldr709@...il.com>
> >
> >lockdep_assert_held() is better suited to checking locking requirements,
> >since it only checks if the current thread holds the lock regardless of
> >whether someone else does. This is also a step towards possibly removing
> >spin_is_locked().
> 
> So fyi I'm not crazy about these kind of patches simply because lockdep
> is a lot less used out of anything that's not a lab, and we can be missing
> potential offenders. There's obviously nothing wrong about what you describe
> above perse, just my two cents.

Fair point!

One countervailing advantage of lockdep is that it is not subject to the
false negatives that can happen if someone else happens to be currently
holding the lock.  But what would you suggest instead?

							Thanx, Paul