[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <edadb690-e791-0e9c-e641-ea8876abe96e@huaweicloud.com>
Date: Thu, 26 Jan 2023 12:30:14 +0100
From: Jonas Oberhauser <jonas.oberhauser@...weicloud.com>
To: Alan Stern <stern@...land.harvard.edu>
Cc: "Paul E. McKenney" <paulmck@...nel.org>,
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: [Patch 2/2] tools/memory-model: Provide exact SRCU semantics
On 1/25/2023 11:52 PM, Alan Stern wrote:
> On Wed, Jan 25, 2023 at 10:04:29PM +0100, Jonas Oberhauser wrote:
>>
>> On 1/25/2023 9:21 PM, Alan Stern wrote:
>>> (* Validate nesting *)
>>> flag ~empty Srcu-lock \ domain(srcu-rscs) as unmatched-srcu-lock
>>> flag ~empty Srcu-unlock \ range(srcu-rscs) as unmatched-srcu-unlock
>>> +flag ~empty (srcu-rscs^-1 ; srcu-rscs) \ id as multiple-srcu-matches
>> [...]
>>> // SRCU
>>> -srcu_read_lock(X) __srcu{srcu-lock}(X)
>>> -srcu_read_unlock(X,Y) { __srcu{srcu-unlock}(X,Y); }
>>> +srcu_read_lock(X) __load{srcu-lock}(*X)
>>> +srcu_read_unlock(X,Y) { __store{srcu-unlock}(*X,Y); }
>>> +srcu_down_read(X) __load{srcu-lock}(*X)
>>> +srcu_up_read(X,Y) { __store{srcu-unlock}(*X,Y); }
>> How do you feel about introducing Srcu-up and Srcu-down with this patch?
> Why invent new classes for them? They are literally the same operation
> as Srcu-lock and Srcu-unlock; the only difference is how the kernel's
> lockdep checker treats them.
I don't think they're necessarily implemented in a compatible way, so
r = srcu_lock(s);
srcu_up(s,r);
might not actually work, but would currently be ok'ed by LKMM. With
different classes you could state
flag ~empty [Srcu-lock];srcu-rscs;[Srcu-up] as srcu-mismatch-lock-to-up
flag ~empty [Srcu-down];srcu-rscs;[Srcu-unlock] as
srcu-mismatch-down-to-unlock
I think with the current implementation this code might work, but I
don't feel like this is inherently true.
You could then also go ahead and define the "same CPU" requirement as a
flag for lock and unlock specifically, like
flag ~empty [Srcu-lock];srcu-rscs & ext as srcu-lock-unlock-mismatch-CPU
or so.
Best wishes, jonas
Powered by blists - more mailing lists