linux-kernel - Re: Question about PB rule of LKMM

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Message-ID: <ZejC+lutRuwXQrMz@andrea>
Date: Wed, 6 Mar 2024 20:24:42 +0100
From: Andrea Parri <parri.andrea@...il.com>
To: Alan Stern <stern@...land.harvard.edu>
Cc: Kenneth-Lee-2012@...mail.com, linux-kernel@...r.kernel.org,
	paulmck@...nel.org
Subject: Re: Question about PB rule of LKMM

> Later on, the file includes this paragraph, which answers the question 
> you were asking:
> 
> ---------------------------------------------------------------------
> The existence of a pb link from E to F implies that E must execute
> before F.  To see why, suppose that F executed first.  Then W would
> have propagated to E's CPU before E executed.  If E was a store, the
> memory subsystem would then be forced to make E come after W in the
> coherence order, contradicting the fact that E ->coe W.  If E was a
> load, the memory subsystem would then be forced to satisfy E's read
> request with the value stored by W or an even later store,
> contradicting the fact that E ->fre W.
> ---------------------------------------------------------------------

TBF, that just explains (not F ->xb E), or I guess that was the origin
of the question.

  Andrea