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Date: Wed, 13 Aug 2014 13:50:24 -0400
From: Rik van Riel <riel@redhat.com>
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To: Peter Zijlstra <peterz@infradead.org>, Oleg Nesterov <oleg@redhat.com>
CC: linux-kernel@vger.kernel.org,
        Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>,
        Frank Mayhar <fmayhar@google.com>,
        Frederic Weisbecker <fweisbec@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Sanjay Rao <srao@redhat.com>, Larry Woodman <lwoodman@redhat.com>
Subject: Re: [PATCH RFC] time: drop do_sys_times spinlock
References: <20140812142539.01851e52@annuminas.surriel.com> <20140812191218.GA15210@redhat.com> <53EA94DD.5040900@redhat.com> <20140813172230.GA6296@redhat.com> <20140813174048.GV9918@twins.programming.kicks-ass.net>
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On 08/13/2014 01:40 PM, Peter Zijlstra wrote:

> So the problem with the above is the lack of fwd progress; if
> there's enough clone()/exit() happening in the thread group (and
> the more CPUs the more possible), we'll keep repeating.

We can fall back to taking the lock if we circle around,
or if there is a writer active when we are in seqcount_read,
similar to what the semaphore (ipc/sem.c) code is doing.

read_seqbegin_or_lock would do the trick...
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