From: Alan Stern <stern@rowland.harvard.edu>
To: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: LKMM Maintainers -- Akira Yokosawa <akiyks@gmail.com>,
Andrea Parri <andrea.parri@amarulasolutions.com>,
Boqun Feng <boqun.feng@gmail.com>,
Daniel Lustig <dlustig@nvidia.com>,
David Howells <dhowells@redhat.com>,
Jade Alglave <j.alglave@ucl.ac.uk>,
Luc Maranget <luc.maranget@inria.fr>,
Nicholas Piggin <npiggin@gmail.com>,
Peter Zijlstra <peterz@infradead.org>,
Will Deacon <will.deacon@arm.com>,
Kernel development list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/3] tools/memory-model: Add SRCU support
Date: Fri, 16 Nov 2018 10:34:34 -0500 (EST) [thread overview]
Message-ID: <Pine.LNX.4.44L0.1811161029550.1487-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <20181116064310.GU4170@linux.ibm.com>
On Thu, 15 Nov 2018, Paul E. McKenney wrote:
> On Thu, Nov 15, 2018 at 11:19:24AM -0500, Alan Stern wrote:
> > Paul and other LKMM maintainers:
> >
> > The following series of patches adds support for SRCU to the Linux
> > Kernel Memory Model. That is, it adds the srcu_read_lock(),
> > srcu_read_unlock(), and synchronize_srcu() primitives to the model.
> >
> > Patch 1/3 does some renaming of the RCU parts of the
> > memory model's existing CAT code, to help distinguish them
> > from the upcoming SRCU parts.
> >
> > Patch 2/3 refactors the definitions of some RCU relations
> > in the CAT code, in a way that the SRCU portions will need.
> >
> > Patch 3/3 actually adds the SRCU support.
> >
> > This new code requires herd7 version 7.51+4(dev) or later (now
> > available in the herdtools7 github repository) to run. Thanks to Luc
> > for making the necessary changes to support SRCU.
>
> These patches pass the tests that I have constructed, and also regression
> tests, very nice! Applied and pushed, thank you.
>
> > The code does not check that the index argument passed to
> > srcu_read_unlock() is the same as the value returned by the
> > corresponding srcu_read_lock() call. This is deemed to be a semantic
> > issue, not directly relevant to the memory model.
>
> Agreed.
>
> If I understand correctly, there are in theory some use cases that these
> patches do not support, for example:
>
> r1 = srcu_read_lock(a);
> do_1();
> r2 = srcu_read_lock(a);
> do_2();
> srcu_read_unlock(a, r1);
> do_3();
> srcu_read_unlock(a, r2);
Yes, this sort of thing will be misinterpreted as two nested critical
sections rather than two overlapping critical sections.
> In practice, I would be more worried about this had I ever managed to
> find a non-bogus use case for this pattern. ;-)
The example is also a little difficult for humans to follow, at least
without an explanatory comment.
Alan
next prev parent reply other threads:[~2018-11-16 15:34 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-15 16:19 [PATCH 0/3] tools/memory-model: Add SRCU support Alan Stern
2018-11-16 6:43 ` Paul E. McKenney
2018-11-16 15:34 ` Alan Stern [this message]
2018-11-19 12:01 ` Andrea Parri
2018-11-26 22:35 ` Paul E. McKenney
2018-11-27 0:26 ` Andrea Parri
2018-11-27 17:17 ` Paul E. McKenney
2018-11-27 22:34 ` Akira Yokosawa
2018-11-28 0:08 ` Paul E. McKenney
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=Pine.LNX.4.44L0.1811161029550.1487-100000@iolanthe.rowland.org \
--to=stern@rowland.harvard.edu \
--cc=akiyks@gmail.com \
--cc=andrea.parri@amarulasolutions.com \
--cc=boqun.feng@gmail.com \
--cc=dhowells@redhat.com \
--cc=dlustig@nvidia.com \
--cc=j.alglave@ucl.ac.uk \
--cc=linux-kernel@vger.kernel.org \
--cc=luc.maranget@inria.fr \
--cc=npiggin@gmail.com \
--cc=paulmck@linux.ibm.com \
--cc=peterz@infradead.org \
--cc=will.deacon@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).