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SubjectRe: [PATCH 0/3] tools/memory-model: Add SRCU support
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On 2018/11/27 09:17:46 -0800, Paul E. McKenney wrote:
> On Tue, Nov 27, 2018 at 01:26:42AM +0100, Andrea Parri wrote:
>>> 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>
>
> Thank you, applied!
>
> I moved this commit and Alan's three SRCU commits to the branch destined
> for the upcoming merge window.

We need to bump the version of herdtools7 in "REQUIREMENTS". Would it be
7.52?

Removing the explicit version number might be a better idea. Just
say "The latest version of ...".

Thoughts?

Thanks, Akira
>
> Thanx, Paul
>
>> 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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