linux-kernel - Re: Internal vs. external barriers (was: Re: Interesting LKMM litmus test)

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Message-ID: <f2ee717f-586f-7ffe-7729-64c88ab36cad@huaweicloud.com>
Date:   Fri, 20 Jan 2023 21:56:36 +0100
From:   Jonas Oberhauser <jonas.oberhauser@...weicloud.com>
To:     paulmck@...nel.org
Cc:     Andrea Parri <parri.andrea@...il.com>,
        Jonas Oberhauser <jonas.oberhauser@...wei.com>,
        Peter Zijlstra <peterz@...radead.org>, will <will@...nel.org>,
        "boqun.feng" <boqun.feng@...il.com>, npiggin <npiggin@...il.com>,
        dhowells <dhowells@...hat.com>,
        "j.alglave" <j.alglave@....ac.uk>,
        "luc.maranget" <luc.maranget@...ia.fr>, akiyks <akiyks@...il.com>,
        dlustig <dlustig@...dia.com>, joel <joel@...lfernandes.org>,
        urezki <urezki@...il.com>,
        quic_neeraju <quic_neeraju@...cinc.com>,
        frederic <frederic@...nel.org>,
        Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: Internal vs. external barriers (was: Re: Interesting LKMM litmus
 test)



On 1/20/2023 4:32 PM, Paul E. McKenney wrote:
> On Fri, Jan 20, 2023 at 01:51:01PM +0100, Jonas Oberhauser wrote:
>> I'm not going to get it right today, am I?
> Believe me, I know that feeling!  Open-source development is therefore
> an extremely good character-building exercise.  At least that is what
> I keep telling myself.  ;-)

"Calvin, go do something you hate! Being miserable builds character!"

>
>> +let srcu-rscs = ([Srcu-lock] ; (data ; [~ Srcu-unlock] ; rfe) * ; data ;
>> [Srcu-unlock]) & loc
>>
>> I see now that I copied the format from your message but without realizing
>> the original had a `|` where I have a `;`.
>> I hope this version is finally right and perhaps more natural than the (data
>> | rf) version, considering rf can't actually appear in most places and this
>> more closely matches carry-dep;data.
>> But of course feel free to use
>> +let srcu-rscs = ([Srcu-lock] ; (data  | [~ Srcu-unlock] ; rf)+ ;
>> [Srcu-unlock]) & loc
>> instead if you prefer.
>
> The reason for favoring "rf" over "rfe" is the possibility of a litmus
> test where the process containing the srcu_down_read() sometimes but
> not always also has the matching srcu_up_read().  Perhaps a pair of "if"
> statements control which process does the matching srcu_up_read().

If you put the redefinition of data early enough to affect this 
definition, the rfi option should be covered by the carry-dep in the 
redefinition of data, so I left it out.

> And thank you!!!

always ;-)

jonas