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SubjectRe: [PATCH 0/3] tools/memory-model: Add SRCU support
> commit 72f61917f12236514a70017d1ebafb9b8d34a9b6
> Author: Paul E. McKenney <paulmck@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 <paulmck@linux.ibm.com>

Indeed!,

Acked-by: Andrea Parri <andrea.parri@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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