linux-kernel - Re: [RFC] Potential problem in qspinlock due to mixed-size accesses

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Message-ID: <6ac81900-873e-415e-b5b2-96e9f7689468@rowland.harvard.edu>
Date: Thu, 19 Jun 2025 10:32:47 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Thomas Haas <t.haas@...bs.de>
Cc: Andrea Parri <parri.andrea@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Will Deacon <will@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
	Nicholas Piggin <npiggin@...il.com>,
	David Howells <dhowells@...hat.com>,
	Jade Alglave <j.alglave@....ac.uk>,
	Luc Maranget <luc.maranget@...ia.fr>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Akira Yokosawa <akiyks@...il.com>,
	Daniel Lustig <dlustig@...dia.com>,
	Joel Fernandes <joelagnelf@...dia.com>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	lkmm@...ts.linux.dev, hernan.poncedeleon@...weicloud.com,
	jonas.oberhauser@...weicloud.com,
	"r.maseli@...bs.de" <r.maseli@...bs.de>
Subject: Re: [RFC] Potential problem in qspinlock due to mixed-size accesses

On Thu, Jun 19, 2025 at 04:27:56PM +0200, Thomas Haas wrote:
> I support this endeavor, but from the Dartagnan side :).
> We already support MSA in real C/Linux code and so extending our supported
> Litmus fragment to MSA does not sound too hard to me.
> We are just missing a LKMM cat model that supports MSA.

To me, it doesn't feel all that easy.  I'm not even sure where to start 
changing the LKMM.\

Probably the best way to keep things organized would be to begin with 
changes to the informal operational model and then figure out how to 
formalize them.  But what changes are needed to the operational model?

Alan