linux-kernel - Re: [PATCH] tools/memory-model: Add documentation about SRCU read-side critical sections

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Date:   Fri, 24 Feb 2023 11:32:49 +0900
From:   Akira Yokosawa <akiyks@...il.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org, Boqun Feng <boqun.feng@...il.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>,
        Andrea Parri <parri.andrea@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        David Howells <dhowells@...hat.com>,
        Jonas Oberhauser <jonas.oberhauser@...wei.com>,
        linux-arch@...r.kernel.org, Nicholas Piggin <npiggin@...il.com>,
        Paul Heidekrüger <paul.heidekrueger@...tum.de>,
        Will Deacon <will@...nel.org>,
        Akira Yokosawa <akiyks@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH] tools/memory-model: Add documentation about SRCU
 read-side critical sections

Hi Alan,

One minor nit.  Please find inline comment below.

On Wed, 22 Feb 2023 21:36:04 -0500, Alan Stern wrote:
> Expand the discussion of SRCU and its read-side critical sections in
> the Linux Kernel Memory Model documentation file explanation.txt.  The
> new material discusses recent changes to the memory model made in
> commit 6cd244c87428 ("tools/memory-model: Provide exact SRCU
> semantics").
> 
> Signed-off-by: Alan Stern <stern@...land.harvard.edu>
> Cc: Andrea Parri <andrea.parri@...rulasolutions.com>
> Cc: Boqun Feng <boqun.feng@...il.com>
> Cc: Jade Alglave <j.alglave@....ac.uk>
> Cc: Luc Maranget <luc.maranget@...ia.fr>
> Cc: "Paul E. McKenney" <paulmck@...ux.ibm.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Jonas Oberhauser <jonas.oberhauser@...wei.com>
> 
> ---
> 
> Joel, please feel free to add your Co-developed-by and Signed-off-by
> tags to this patch.
> 
>  tools/memory-model/Documentation/explanation.txt |  178 +++++++++++++++++++++--
>  1 file changed, 167 insertions(+), 11 deletions(-)
> 
> Index: usb-devel/tools/memory-model/Documentation/explanation.txt
> ===================================================================
> --- usb-devel.orig/tools/memory-model/Documentation/explanation.txt
> +++ usb-devel/tools/memory-model/Documentation/explanation.txt
> @@ -28,9 +28,10 @@ Explanation of the Linux-Kernel Memory C
>    20. THE HAPPENS-BEFORE RELATION: hb
>    21. THE PROPAGATES-BEFORE RELATION: pb
>    22. RCU RELATIONS: rcu-link, rcu-gp, rcu-rscsi, rcu-order, rcu-fence, and rb
> -  23. LOCKING
> -  24. PLAIN ACCESSES AND DATA RACES
> -  25. ODDS AND ENDS
> +  23. SRCU READ-SIDE CRITICAL SECTIONS
> +  24. LOCKING
> +  25. PLAIN ACCESSES AND DATA RACES
> +  26. ODDS AND ENDS
>  
>  
>  
> @@ -1848,14 +1849,169 @@ section in P0 both starts before P1's gr
>  before it does, and the critical section in P2 both starts after P1's
>  grace period does and ends after it does.
>  
> -Addendum: The LKMM now supports SRCU (Sleepable Read-Copy-Update) in
> -addition to normal RCU.  The ideas involved are much the same as
> -above, with new relations srcu-gp and srcu-rscsi added to represent
> -SRCU grace periods and read-side critical sections.  There is a
> -restriction on the srcu-gp and srcu-rscsi links that can appear in an
> -rcu-order sequence (the srcu-rscsi links must be paired with srcu-gp
> -links having the same SRCU domain with proper nesting); the details
> -are relatively unimportant.
> +The LKMM supports SRCU (Sleepable Read-Copy-Update) in addition to
> +normal RCU.  The ideas involved are much the same as above, with new
> +relations srcu-gp and srcu-rscsi added to represent SRCU grace periods
> +and read-side critical sections.  However, there are some important
> +differences between RCU read-side critical sections and their SRCU
> +counterparts, as described in the next section.
> +
> +
> +SRCU READ-SIDE CRITICAL SECTIONS
> +--------------------------------
> +
> +The LKMM models uses the srcu-rscsi relation to model SRCU read-side

I think you mean either:

   The LKMM models the srcu-rscsi relation ...

or: 

   The LKMM uses the srcu-rscsi relation ...

With this fixed,

Reviewed-by: Akira Yokosawa <akiyks@...il.com>

> +critical sections.  They are different from RCU read-side critical
> +sections in the following respects:
> +
[...]

        Thanks, Akira