linux-kernel - Re: [PATCH v2] tools/memory-model: Make compat with herd7 7.47 ("-" -> "

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Date:   Tue, 20 Feb 2018 06:57:20 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Akira Yokosawa <akiyks@...il.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        stern@...land.harvard.edu, parri.andrea@...il.com,
        will.deacon@....com, peterz@...radead.org, boqun.feng@...il.com,
        npiggin@...il.com, dhowells@...hat.com, j.alglave@....ac.uk,
        luc.maranget@...ia.fr, Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [PATCH v2] tools/memory-model: Make compat with herd7 7.47 ("-"
 -> "_")

On Mon, Feb 19, 2018 at 12:46:51AM +0900, Akira Yokosawa wrote:
> On 2018/02/14 14:52:38 -0800, Paul E. McKenney wrote:
> > On Thu, Feb 15, 2018 at 07:20:35AM +0900, Akira Yokosawa wrote:
> >> On 2018/02/09 17:07:03 -0800, Paul E. McKenney wrote:
> >>> On Sat, Feb 10, 2018 at 08:46:25AM +0900, Akira Yokosawa wrote:
> >>>> >From 7c1f497a9a51e8db1a94c8a7ef0b74b235aaab88 Mon Sep 17 00:00:00 2001
> >>>> From: Akira Yokosawa <akiyks@...il.com>
> >>>> Date: Fri, 9 Feb 2018 04:51:05 -0800
> >>>> Subject: [PATCH v2] tools/memory-model: Make compat with herd7 7.47 ("-" -> "_")
> >>>>
> >>>> As of herd7 7.47, these '-'s are not permitted and end up in
> >>>> errors such as:
> >>>>
> >>>>     File "./linux-kernel.def", line 44, characters 29-30:
> >>>>     unexpected '-' (in macros)
> >>>>
> >>>> Partial revert of commit 2d5fba7782d6 ("linux-kernel*: Make RCU
> >>>> identifiers match ASPLOS paper") in the repository at
> >>>> https://github.com/aparri/memory-model can restore the compatibility
> >>>> with herd7 7.47.
> >>>>
> >>>> Reported-by: Patrick Bellasi <patrick.bellasi@....com>
> >>>> Suggested-by: Andrea Parri <parri.andrea@...il.com>
> >>>> Signed-off-by: Akira Yokosawa <akiyks@...il.com>
> >>>> ---
> >>>> Paul,
> >>>>
> >>>> FWIW, this is a squashed version relative to patch 07/10 in the RFC series.
> >>>
> >>> Thank you, Akira!
> >>>
> >>> I am going to hold off on this for a bit to see if we can instead get
> >>> a new release of herd7, but if we can't. this might well be a very good
> >>> way to go.
> >>
> >> So, herdtools7.7.48 is now available by "opam update; opam upgrade".
> >> Maybe mentioning the required version of herdtools7 in README would help.
> > 
> > Or have some way for the memory model's .cat files to state what version
> > they need, but in the meantime please see the patch below.  But even with
> > such version specification, we probably want to have the version in the
> > README...
> > 
> >> One glitch I'm aware of is one of the output of klitmus7 fails to
> >> compile on kernels prior to 4.14, because of smp_mb__after_spinlock()
> >> used in Z6.0+pooncelock+poonceLock+pombonce.litmus.
> > 
> > This is one advantage of having the memory model in the kernel source
> > itself -- the versions match.  And people can always fire up a different
> > kernel version (for example, within a VM) to run the output of klitmus7.
> > 
> 
> There is another unfortunate mismatch in kernel and herdtools7 updates.
> 
> klitmus7 in herdtools7 7.48 requires definition of ACCESS_ONCE() in kernel
> headers, but it has been removed in Linux 4.15. This means klitmus7 of
> herdtools7 7.48 works only on Linux 4.14.
> 
> In the repository of herdtools7, with the suggestion of Andrea, commit
> e87d7f9287d1 ("klitmus: Use WRITE_ONCE and READ_ONCE in place of deprecated
> ACCESS_ONCE in "user" synchronization barrier") has addressed the issue. 
> 
> This series is intended to be merged in Linux 4.17 merge window,
> and hopefully we can have another update of herdtools7 by the time the merge
> window opens...
> 
> Dependency to out-of-tree tools looks quite tricky. We need some neat way to
> manage things.
> 
> Umm...

Yes, dependencies on out-of-tree tools is quite tricky, witness the
"fun and excitement" provided even by GCC from time to time.

I agree that another herdtools7 release is required, and I do very much
thank you for testing this and finding this issue!

							Thanx, Paul