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Re: [RFC][PATCH 0/5] arch: atomic rework
- From: "Paul E. McKenney" <paulmck at linux dot vnet dot ibm dot com>
- To: Linus Torvalds <torvalds at linux-foundation dot org>
- Cc: Torvald Riegel <triegel at redhat dot com>, Will Deacon <will dot deacon at arm dot com>, Peter Zijlstra <peterz at infradead dot org>, Ramana Radhakrishnan <Ramana dot Radhakrishnan at arm dot com>, David Howells <dhowells at redhat dot com>, "linux-arch at vger dot kernel dot org" <linux-arch at vger dot kernel dot org>, "linux-kernel at vger dot kernel dot org" <linux-kernel at vger dot kernel dot org>, "akpm at linux-foundation dot org" <akpm at linux-foundation dot org>, "mingo at kernel dot org" <mingo at kernel dot org>, "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
- Date: Thu, 20 Feb 2014 01:20:49 -0800
- Subject: Re: [RFC][PATCH 0/5] arch: atomic rework
- Authentication-results: sourceware.org; auth=none
- References: <20140218030002 dot GA15857 at linux dot vnet dot ibm dot com> <CA+55aFyqLrj4d2TA+2aazRqXnbVsUvs0yaBL2D5rXF1G=Kiu_g at mail dot gmail dot com> <CA+55aFwsq5E8kMoEeHJJ1f2=+QAUCu_HndfPxHNz8fUBprS-jQ at mail dot gmail dot com> <1392740258 dot 18779 dot 7732 dot camel at triegel dot csb> <CA+55aFw7QYEMFs0BCxqRJW3Cz=tLbaku-tmN6hLXPKP9jbom7Q at mail dot gmail dot com> <1392752867 dot 18779 dot 8120 dot camel at triegel dot csb> <CA+55aFxQPxQ8WOaZL8yAqBA=Y4k2gDn4r4oepMyi0uL6XLzv3w at mail dot gmail dot com> <20140220040102 dot GM4250 at linux dot vnet dot ibm dot com> <CA+55aFwwscSzwTr+xRdirtTx7HzugmMY9HrDe0GBqNhn=AuNVA at mail dot gmail dot com> <20140220083032 dot GN4250 at linux dot vnet dot ibm dot com>
- Reply-to: paulmck at linux dot vnet dot ibm dot com
On Thu, Feb 20, 2014 at 12:30:32AM -0800, Paul E. McKenney wrote:
> On Wed, Feb 19, 2014 at 08:43:14PM -0800, Linus Torvalds wrote:
[ . . . ]
> So, if you make one of two changes to your example, then I will agree
> with you. The first change is to have a real data dependency between
> the read of "a" and the second read:
>
> - Initial state:
>
> a = &c, b = 0; c = 0;
>
> - Thread 1 ("consumer"):
>
> if (atomic_read(&a, consume))
And the above should be "if (atomic_read(&a, consume) != &c)". Sigh!!!
Thanx, Paul
> return *a;
> /* not yet initialized */
> return -1;
>
> - Thread 2 ("initializer"):
>
> b = some_value_lets_say_42;
> /* We are now ready to party */
> atomic_write(&a, &b, release);