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Date:   Thu, 23 Mar 2023 11:45:23 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Andrea Parri <parri.andrea@gmail.com>
Cc:     stern@rowland.harvard.edu, will@kernel.org, peterz@infradead.org,
        boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com,
        j.alglave@ucl.ac.uk, luc.maranget@inria.fr, akiyks@gmail.com,
        dlustig@nvidia.com, joel@joelfernandes.org,
        linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org
Subject: Re: [PATCH] tools/memory-model: Remove out-of-date SRCU documentation
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On Thu, Mar 23, 2023 at 02:37:51AM +0100, Andrea Parri wrote:
> Commit 6cd244c87428 ("tools/memory-model: Provide exact SRCU semantics")
> changed the semantics of partially overlapping SRCU read-side critical
> sections (among other things), making such documentation out-of-date.
> The new, semantic changes are discussed in explanation.txt.  Remove the
> out-of-date documentation.
> 
> Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> Acked-by: Alan Stern <stern@rowland.harvard.edu>

Applied, thank you all!

							Thanx, Paul

> ---
>  .../Documentation/litmus-tests.txt            | 27 +------------------
>  1 file changed, 1 insertion(+), 26 deletions(-)
> 
> diff --git a/tools/memory-model/Documentation/litmus-tests.txt b/tools/memory-model/Documentation/litmus-tests.txt
> index 26554b1c5575e..acac527328a1f 100644
> --- a/tools/memory-model/Documentation/litmus-tests.txt
> +++ b/tools/memory-model/Documentation/litmus-tests.txt
> @@ -1028,32 +1028,7 @@ Limitations of the Linux-kernel memory model (LKMM) include:
>  		additional call_rcu() process to the site of the
>  		emulated rcu-barrier().
>  
> -	e.	Although sleepable RCU (SRCU) is now modeled, there
> -		are some subtle differences between its semantics and
> -		those in the Linux kernel.  For example, the kernel
> -		might interpret the following sequence as two partially
> -		overlapping SRCU read-side critical sections:
> -
> -			 1  r1 = srcu_read_lock(&my_srcu);
> -			 2  do_something_1();
> -			 3  r2 = srcu_read_lock(&my_srcu);
> -			 4  do_something_2();
> -			 5  srcu_read_unlock(&my_srcu, r1);
> -			 6  do_something_3();
> -			 7  srcu_read_unlock(&my_srcu, r2);
> -
> -		In contrast, LKMM will interpret this as a nested pair of
> -		SRCU read-side critical sections, with the outer critical
> -		section spanning lines 1-7 and the inner critical section
> -		spanning lines 3-5.
> -
> -		This difference would be more of a concern had anyone
> -		identified a reasonable use case for partially overlapping
> -		SRCU read-side critical sections.  For more information
> -		on the trickiness of such overlapping, please see:
> -		https://paulmck.livejournal.com/40593.html
> -
> -	f.	Reader-writer locking is not modeled.  It can be
> +	e.	Reader-writer locking is not modeled.  It can be
>  		emulated in litmus tests using atomic read-modify-write
>  		operations.
>  
> -- 
> 2.34.1
>