From: Peter Zijlstra <peterz@infradead.org>
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, Davidlohr Bueso <dbueso@suse.de>
Subject: Re: [PATCH] rbtree: use READ_ONCE in RB_EMPTY_ROOT
Date: Tue, 12 Jan 2016 16:59:31 +0100 [thread overview]
Message-ID: <20160112155931.GM6357@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20160112150946.GA1927@linux-uzut.site>
On Tue, Jan 12, 2016 at 07:09:46AM -0800, Davidlohr Bueso wrote:
> On Tue, 12 Jan 2016, Peter Zijlstra wrote:
>
> >On Mon, Jan 11, 2016 at 10:22:43AM -0800, Davidlohr Bueso wrote:
> >>With d72da4a4d97 (rbtree: Make lockless searches non-fatal) our rbtrees
> >>provide weak guarantees that allows us to do lockless (and very speculative)
> >>reads of the tree. Such readers cannot see partial stores on nodes, ie
> >>left/right as well as root. As such, similar to the WRITE_ONCE semantics when
> >>doing rotations, use READ_ONCE when checking the root node in RB_EMPTY_ROOT.
> >
> >No objection, but is this actually used anywhere?
>
> I found this because I wanted to use the waiter check in rtmutexes in a lockless
> fashion (ie rt_mutex_has_waiters).
OK, fair enough.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
prev parent reply other threads:[~2016-01-12 15:59 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-11 18:22 [PATCH] rbtree: use READ_ONCE in RB_EMPTY_ROOT Davidlohr Bueso
2016-01-12 9:06 ` Peter Zijlstra
2016-01-12 15:09 ` Davidlohr Bueso
2016-01-12 15:59 ` Peter Zijlstra [this message]
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