linux-kernel - Re: [PATCH v2 2/2] tools/memory-model: Make ppo a subrelation of po

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Message-ID: <Y9aoA2UxvWyNwOtx@andrea>
Date:   Sun, 29 Jan 2023 18:11:12 +0100
From:   Andrea Parri <parri.andrea@...il.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Jonas Oberhauser <jonas.oberhauser@...weicloud.com>,
        paulmck@...nel.org, will@...nel.org, peterz@...radead.org,
        boqun.feng@...il.com, npiggin@...il.com, dhowells@...hat.com,
        j.alglave@....ac.uk, luc.maranget@...ia.fr, akiyks@...il.com,
        dlustig@...dia.com, joel@...lfernandes.org, urezki@...il.com,
        quic_neeraju@...cinc.com, frederic@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] tools/memory-model: Make ppo a subrelation of po

> The reason why Wx=1 ->ww-vis Wx=2:
> 
> 	0:Wx=1 ->po-rel 0:Wy=1 and po-rel < fence < ww-post-bounded.
> 
> 	0:Wy=1 ->rfe 1:Ry=1 ->(hb* & int) 1:Rdy=1 and
> 		(rfe ; hb* & int) <= (rfe ; xbstar & int) <= vis.
> 
> 	1:Rdy=1 ->po 1:unlock ->rfe 3:lock ->po 3:Wx=2
> 		so 1:Rdy=1 ->po-unlock-lock-po 3:Wx=2
> 		and po-unlock-lock-po <= mb <= fence <= w-pre-bounded.
> 
> Finally, w-post-bounded ; vis ; w-pre-bounded <= ww-vis.

To clarify, po-unlock-lock-po is not a subrelation of mb; see what
happens without the smp_mb__after_unlock_lock().

  Andrea