> commit 72f61917f12236514a70017d1ebafb9b8d34a9b6
> Author: Paul E. McKenney <paul...@linux.ibm.com>
> Date:   Mon Nov 26 14:26:43 2018 -0800
> 
>     tools/memory-model: Update README for addition of SRCU
>     
>     This commit updates the section on LKMM limitations to no longer say
>     that SRCU is not modeled, but instead describe how LKMM's modeling of
>     SRCU departs from the Linux-kernel implementation.
>     
>     TL;DR:  There is no known valid use case that cares about the Linux
>     kernel's ability to have partially overlapping SRCU read-side critical
>     sections.
>     
>     Signed-off-by: Paul E. McKenney <paul...@linux.ibm.com>

Indeed!,

Acked-by: Andrea Parri <andrea.pa...@amarulasolutions.com>

  Andrea


> 
> diff --git a/tools/memory-model/README b/tools/memory-model/README
> index 0f2c366518c6..9d7d4f23503f 100644
> --- a/tools/memory-model/README
> +++ b/tools/memory-model/README
> @@ -221,8 +221,29 @@ The Linux-kernel memory model has the following 
> limitations:
>               additional call_rcu() process to the site of the
>               emulated rcu-barrier().
>  
> -     e.      Sleepable RCU (SRCU) is not modeled.  It can be
> -             emulated, but perhaps not simply.
> +     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,
> +             please see: https://paulmck.livejournal.com/40593.html
>  
>       f.      Reader-writer locking is not modeled.  It can be
>               emulated in litmus tests using atomic read-modify-write
> 

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