linux-kernel - Re: RCU tests for Maple Tree

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Date:   Mon, 17 May 2021 16:30:53 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     "Paul E. McKenney" <paulmck@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: RCU tests for Maple Tree

* Paul E. McKenney <paulmck@...nel.org> [210517 11:40]:
> Hello, Liam!
> 
> Apologies for my being so slow here, but just wanted to double-check my
> understanding of this code.
> 
> There appear to be two tests that execute from run_check_rcu():
> 
> o	rcu_loop().  This appears to have RCU readers scanning the tree
> 	while an updater is adding a single range.  (Or replacing it,
> 	as the case might be.)
> 
> o	rcu_val().  This appears to have RCU readers repeatedly reading a
> 	given value while an updater is adding/replacing a single range.
> 	The test complains if no one sees the new value.
> 
> These tests appear to be the only use of threads, though perhaps the
> test harness has some way of creating threads that I missed.
> 
> Are there other tests that I should be looking for?

No, those are the only ones I'm running with threads right now.  I think
all RCU tests are run from check_rcu() iirc.  This did yield results of
failures that had to be addressed so I'm somewhat confident that it's
actually working.

>From your wording I'm gathering I need to increase this by a lot more
test cases?

Thanks,
Liam