From: Jonas Oberhauser <jonas.oberhauser@huaweicloud.com>
To: paulmck@kernel.org, Alan Stern <stern@rowland.harvard.edu>
Cc: Andrea Parri <parri.andrea@gmail.com>,
Jonas Oberhauser <jonas.oberhauser@huawei.com>,
Peter Zijlstra <peterz@infradead.org>, will <will@kernel.org>,
"boqun.feng" <boqun.feng@gmail.com>, npiggin <npiggin@gmail.com>,
dhowells <dhowells@redhat.com>, "j.alglave" <j.alglave@ucl.ac.uk>,
"luc.maranget" <luc.maranget@inria.fr>, akiyks <akiyks@gmail.com>,
dlustig <dlustig@nvidia.com>, joel <joel@joelfernandes.org>,
urezki <urezki@gmail.com>,
quic_neeraju <quic_neeraju@quicinc.com>,
frederic <frederic@kernel.org>,
Kernel development list <linux-kernel@vger.kernel.org>
Subject: Re: Internal vs. external barriers (was: Re: Interesting LKMM litmus test)
Date: Fri, 20 Jan 2023 10:20:11 +0100 [thread overview]
Message-ID: <acbbd099-07de-fba9-3d44-874bdfc47365@huaweicloud.com> (raw)
In-Reply-To: <20230120035521.GA319650@paulmck-ThinkPad-P17-Gen-1>
On 1/20/2023 4:55 AM, Paul E. McKenney wrote:
> On Thu, Jan 19, 2023 at 02:51:53PM -0500, Alan Stern wrote:
>> On Thu, Jan 19, 2023 at 10:41:07AM -0800, Paul E. McKenney wrote:
>>> In contrast, this actually needs srcu_down_read() and srcu_up_read():
>>>
>>> ------------------------------------------------------------------------
>>>
>>> C C-srcu-nest-6
>>>
>>> (*
>>> * Result: Never
>>> *
>>> * Flag unbalanced-srcu-locking
>>> * This would be valid for srcu_down_read() and srcu_up_read().
>>> *)
>>>
>>> {}
>>>
>>> P0(int *x, int *y, struct srcu_struct *s1, int *idx)
>>> {
>>> int r2;
>>> int r3;
>>>
>>> r3 = srcu_down_read(s1);
>>> WRITE_ONCE(*idx, r3);
>>> r2 = READ_ONCE(*y);
>>> }
>>>
>>> P1(int *x, int *y, struct srcu_struct *s1, int *idx)
>>> {
>>> int r1;
>>> int r3;
>>>
>>> r1 = READ_ONCE(*x);
>>> r3 = READ_ONCE(*idx);
>>> srcu_up_read(s1, r3);
>>> }
>>>
>>> P2(int *x, int *y, struct srcu_struct *s1)
>>> {
>>> WRITE_ONCE(*y, 1);
>>> synchronize_srcu(s1);
>>> WRITE_ONCE(*x, 1);
>>> }
>>>
>>> locations [0:r1]
>>> exists (1:r1=1 /\ 0:r2=0)
>> I modified this litmus test by adding a flag variable with an
>> smp_store_release in P0, an smp_load_acquire in P1, and a filter clause
>> to ensure that P1 reads the flag and idx from P1.
>>
>> With the patch below, the results were as expected:
>>
>> Test C-srcu-nest-6 Allowed
>> States 3
>> 0:r1=0; 0:r2=0; 1:r1=0;
>> 0:r1=0; 0:r2=1; 1:r1=0;
>> 0:r1=0; 0:r2=1; 1:r1=1;
>> No
>> Witnesses
>> Positive: 0 Negative: 3
>> Condition exists (1:r1=1 /\ 0:r2=0)
>> Observation C-srcu-nest-6 Never 0 3
>> Time C-srcu-nest-6 0.04
>> Hash=2b010cf3446879fb84752a6016ff88c5
>>
>> It turns out that the idea of removing rf edges from Srcu-unlock events
>> doesn't work well. The missing edges mess up herd's calculation of the
>> fr relation and the coherence axiom. So I've gone back to filtering
>> those edges out of carry-dep.
>>
>> Also, Boqun's suggestion for flagging ordinary accesses to SRCU
>> structures no longer works, because the lock and unlock operations now
>> _are_ normal accesses. I removed that check too, but it shouldn't hurt
>> much because I don't expect to encounter litmus tests that try to read
>> or write srcu_structs directly.
>>
>> Alan
>>
>>
>>
>> Index: usb-devel/tools/memory-model/linux-kernel.bell
>> ===================================================================
>> --- usb-devel.orig/tools/memory-model/linux-kernel.bell
>> +++ usb-devel/tools/memory-model/linux-kernel.bell
>> @@ -53,38 +53,30 @@ let rcu-rscs = let rec
>> in matched
>>
>> (* Validate nesting *)
>> -flag ~empty Rcu-lock \ domain(rcu-rscs) as unbalanced-rcu-locking
>> -flag ~empty Rcu-unlock \ range(rcu-rscs) as unbalanced-rcu-locking
>> +flag ~empty Rcu-lock \ domain(rcu-rscs) as unbalanced-rcu-lock
>> +flag ~empty Rcu-unlock \ range(rcu-rscs) as unbalanced-rcu-unlock
>>
>> (* Compute matching pairs of nested Srcu-lock and Srcu-unlock *)
>> -let srcu-rscs = let rec
>> - unmatched-locks = Srcu-lock \ domain(matched)
>> - and unmatched-unlocks = Srcu-unlock \ range(matched)
>> - and unmatched = unmatched-locks | unmatched-unlocks
>> - and unmatched-po = ([unmatched] ; po ; [unmatched]) & loc
>> - and unmatched-locks-to-unlocks =
>> - ([unmatched-locks] ; po ; [unmatched-unlocks]) & loc
>> - and matched = matched | (unmatched-locks-to-unlocks \
>> - (unmatched-po ; unmatched-po))
>> - in matched
>> +let srcu-rscs = ([Srcu-lock] ; (data | rf)+ ; [Srcu-unlock]) & loc
>>
>> (* Validate nesting *)
>> -flag ~empty Srcu-lock \ domain(srcu-rscs) as unbalanced-srcu-locking
>> -flag ~empty Srcu-unlock \ range(srcu-rscs) as unbalanced-srcu-locking
>> +flag ~empty Srcu-lock \ domain(srcu-rscs) as unbalanced-srcu-lock
>> +flag ~empty Srcu-unlock \ range(srcu-rscs) as unbalanced-srcu-unlock
>> +flag ~empty (srcu-rscs^-1 ; srcu-rscs) \ id as multiple-srcu-matches
>>
>> (* Check for use of synchronize_srcu() inside an RCU critical section *)
>> flag ~empty rcu-rscs & (po ; [Sync-srcu] ; po) as invalid-sleep
>>
>> (* Validate SRCU dynamic match *)
>> -flag ~empty different-values(srcu-rscs) as srcu-bad-nesting
>> +flag ~empty different-values(srcu-rscs) as bad-srcu-value-match
>>
>> (* Compute marked and plain memory accesses *)
>> let Marked = (~M) | IW | Once | Release | Acquire | domain(rmw) | range(rmw) |
>> - LKR | LKW | UL | LF | RL | RU
>> + LKR | LKW | UL | LF | RL | RU | Srcu-lock | Srcu-unlock
>> let Plain = M \ Marked
>>
>> (* Redefine dependencies to include those carried through plain accesses *)
>> -let carry-dep = (data ; rfi)*
>> +let carry-dep = (data ; [~ Srcu-unlock] ; rfi)*
>> let addr = carry-dep ; addr
>> let ctrl = carry-dep ; ctrl
>> let data = carry-dep ; data
>> Index: usb-devel/tools/memory-model/linux-kernel.def
>> ===================================================================
>> --- usb-devel.orig/tools/memory-model/linux-kernel.def
>> +++ usb-devel/tools/memory-model/linux-kernel.def
>> @@ -49,8 +49,10 @@ synchronize_rcu() { __fence{sync-rcu}; }
>> synchronize_rcu_expedited() { __fence{sync-rcu}; }
>>
>> // 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); }
>> synchronize_srcu(X) { __srcu{sync-srcu}(X); }
>> synchronize_srcu_expedited(X) { __srcu{sync-srcu}(X); }
> And for some initial tests:
>
> https://github.com/paulmckrcu/litmus/blob/master/manual/kernel/C-srcu-nest-1.litmus
>
> "Flag multiple-srcu-matches" but otherwise OK.
> As a "hail Mary" exercise, I used r4 for the second SRCU
> read-side critical section, but this had no effect.
> (This flag is expected and seen for #4 below.)
This is because srcu_lock/srcu_unlock are reads and writes, and so you
get the accidental rf relation here I was talking about earlier.
In particular your first lock() is linked by data ; rf ; data to the
second unlock(), which therefore seems to have data coming in from two
sources.
You would be better off moving the carry-dep/data definitions higher in
the file,
-let carry-dep = (data ; rfi)*
+let carry-dep = (data ; [~ Srcu-unlock] ; rfi)*
let addr = carry-dep ; addr
let ctrl = carry-dep ; ctrl
let data = carry-dep ; data
and then defining
+let srcu-rscs = ([Srcu-lock] ; data ; [Srcu-unlock]) & loc
Note here I'm just using the freshly redefined data, instead of the (data;rf)+
best wishes, jonas
next prev parent reply other threads:[~2023-01-20 9:20 UTC|newest]
Thread overview: 161+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20220921173109.GA1214281@paulmck-ThinkPad-P17-Gen-1>
[not found] ` <YytfFiMT2Xsdwowf@rowland.harvard.edu>
[not found] ` <YywXuzZ/922LHfjI@hirez.programming.kicks-ass.net>
[not found] ` <114ECED5-FED1-4361-94F7-8D9BC02449B7>
[not found] ` <YzSAnclenTz7KQyt@rowland.harvard.edu>
[not found] ` <f763bd5ff835458d8750b61da47fe316@huawei.com>
2023-01-03 18:56 ` Internal vs. external barriers (was: Re: Interesting LKMM litmus test) Alan Stern
2023-01-04 15:37 ` Andrea Parri
2023-01-04 20:58 ` Alan Stern
[not found] ` <ee186bc17a5e48298a5373f688496dce@huawei.com>
2023-01-05 17:32 ` Paul E. McKenney
[not found] ` <bea712c82e6346f8973399a5711ff78a@huawei.com>
2023-01-11 15:06 ` Alan Stern
[not found] ` <768ffe7edc7f4ddfacd5b0a8e844ed84@huawei.com>
2023-01-11 17:01 ` Alan Stern
[not found] ` <07579baee4b84532a76ea8b0b33052bb@huawei.com>
2023-01-12 21:57 ` Paul E. McKenney
2023-01-13 16:38 ` Alan Stern
2023-01-13 19:54 ` Paul E. McKenney
[not found] ` <06a8aef7eb8d46bca34521a80880dae3@huawei.com>
2023-01-14 17:42 ` Paul E. McKenney
[not found] ` <e51c82a113484b6bb62354a49376f248@huawei.com>
2023-01-14 16:42 ` Alan Stern
2023-01-17 17:48 ` Jonas Oberhauser
2023-01-17 21:19 ` Alan Stern
2023-01-18 11:25 ` Jonas Oberhauser
2023-01-19 2:28 ` Alan Stern
2023-01-19 11:22 ` Jonas Oberhauser
2023-01-19 16:41 ` Alan Stern
2023-01-19 18:43 ` Paul E. McKenney
2023-01-23 16:16 ` Jonas Oberhauser
2023-01-23 19:58 ` Alan Stern
2023-01-23 20:06 ` Jonas Oberhauser
2023-01-23 20:41 ` Alan Stern
2023-01-24 13:21 ` Jonas Oberhauser
2023-01-24 15:54 ` Jonas Oberhauser
2023-01-24 17:22 ` Alan Stern
[not found] ` <4c1abc7733794519ad7c5153ae8b58f9@huawei.com>
2023-01-13 16:28 ` Alan Stern
2023-01-13 20:07 ` Paul E. McKenney
2023-01-13 20:32 ` Paul E. McKenney
2023-01-14 17:40 ` Alan Stern
2023-01-14 17:48 ` Paul E. McKenney
[not found] ` <136d019d8c8049f6b737627df830e66f@huawei.com>
2023-01-14 17:53 ` Paul E. McKenney
2023-01-14 18:15 ` Paul E. McKenney
2023-01-14 19:58 ` Alan Stern
2023-01-15 5:19 ` Paul E. McKenney
2023-01-14 20:19 ` Alan Stern
2023-01-15 5:15 ` Paul E. McKenney
2023-01-15 16:23 ` Alan Stern
2023-01-15 18:10 ` Paul E. McKenney
2023-01-15 20:46 ` Alan Stern
2023-01-16 4:23 ` Paul E. McKenney
2023-01-16 18:11 ` Alan Stern
2023-01-16 19:06 ` Paul E. McKenney
2023-01-16 19:20 ` Alan Stern
2023-01-16 22:13 ` Paul E. McKenney
2023-01-17 11:46 ` Andrea Parri
2023-01-17 15:14 ` Paul E. McKenney
2023-01-17 15:56 ` Alan Stern
2023-01-17 17:43 ` Paul E. McKenney
2023-01-17 18:27 ` Jonas Oberhauser
2023-01-17 18:55 ` Paul E. McKenney
2023-01-17 20:20 ` Jonas Oberhauser
2023-01-17 20:15 ` Alan Stern
2023-01-18 3:50 ` Paul E. McKenney
2023-01-18 16:50 ` Alan Stern
2023-01-18 19:42 ` Jonas Oberhauser
2023-01-18 20:19 ` Paul E. McKenney
2023-01-18 20:30 ` Jonas Oberhauser
2023-01-18 21:12 ` Paul E. McKenney
2023-01-18 21:24 ` Jonas Oberhauser
2023-01-19 0:11 ` Paul E. McKenney
2023-01-19 13:39 ` Jonas Oberhauser
2023-01-19 18:41 ` Paul E. McKenney
2023-01-19 19:51 ` Alan Stern
2023-01-19 21:53 ` Paul E. McKenney
2023-01-19 22:04 ` Alan Stern
2023-01-19 23:03 ` Paul E. McKenney
2023-01-20 9:43 ` Jonas Oberhauser
2023-01-20 15:39 ` Paul E. McKenney
2023-01-20 20:46 ` Jonas Oberhauser
2023-01-20 21:37 ` Paul E. McKenney
2023-01-20 22:36 ` Jonas Oberhauser
2023-01-20 23:19 ` Paul E. McKenney
2023-01-21 0:03 ` Jonas Oberhauser
2023-01-21 0:34 ` Paul E. McKenney
2023-01-20 3:55 ` Paul E. McKenney
2023-01-20 9:20 ` Jonas Oberhauser [this message]
2023-01-20 12:34 ` Jonas Oberhauser
2023-01-20 12:51 ` Jonas Oberhauser
2023-01-20 15:32 ` Paul E. McKenney
2023-01-20 20:56 ` Jonas Oberhauser
2023-01-20 21:40 ` Paul E. McKenney
2023-01-20 16:14 ` Alan Stern
2023-01-20 17:30 ` Paul E. McKenney
2023-01-20 18:15 ` Alan Stern
2023-01-20 18:59 ` Paul E. McKenney
2023-01-20 10:13 ` Jonas Oberhauser
2023-01-20 15:47 ` Paul E. McKenney
2023-01-20 22:21 ` Jonas Oberhauser
2023-01-20 16:18 ` Alan Stern
2023-01-20 21:41 ` Jonas Oberhauser
2023-01-21 4:38 ` Paul E. McKenney
2023-01-21 17:36 ` Alan Stern
2023-01-21 18:40 ` Paul E. McKenney
2023-01-21 19:56 ` Alan Stern
2023-01-21 20:10 ` Paul E. McKenney
2023-01-21 21:03 ` Alan Stern
2023-01-21 23:49 ` Paul E. McKenney
2023-01-23 11:48 ` Jonas Oberhauser
2023-01-23 15:55 ` Alan Stern
2023-01-23 19:40 ` Jonas Oberhauser
2023-01-23 20:34 ` Alan Stern
2023-01-18 20:06 ` Paul E. McKenney
2023-01-18 20:54 ` Alan Stern
2023-01-18 21:05 ` Jonas Oberhauser
2023-01-19 0:02 ` Paul E. McKenney
2023-01-19 2:19 ` Alan Stern
2023-01-19 11:23 ` Paul E. McKenney
2023-01-20 16:01 ` Alan Stern
2023-01-20 17:58 ` Paul E. McKenney
2023-01-20 18:37 ` Alan Stern
2023-01-20 19:20 ` Paul E. McKenney
2023-01-20 20:36 ` Alan Stern
2023-01-20 21:20 ` Paul E. McKenney
2023-01-22 20:32 ` Alan Stern
2023-01-23 20:16 ` Paul E. McKenney
2023-01-24 2:18 ` Alan Stern
2023-01-24 4:06 ` Paul E. McKenney
2023-01-24 11:09 ` Andrea Parri
2023-01-24 14:54 ` Paul E. McKenney
2023-01-24 15:11 ` Jonas Oberhauser
2023-01-24 16:22 ` Paul E. McKenney
2023-01-24 16:39 ` Jonas Oberhauser
2023-01-24 17:26 ` Paul E. McKenney
2023-01-24 19:30 ` Jonas Oberhauser
2023-01-24 22:15 ` Paul E. McKenney
2023-01-24 22:35 ` Alan Stern
2023-01-24 22:54 ` Paul E. McKenney
2023-01-25 1:54 ` Alan Stern
2023-01-25 2:20 ` Paul E. McKenney
2023-01-25 13:10 ` Jonas Oberhauser
2023-01-25 15:05 ` Paul E. McKenney
2023-01-25 15:34 ` Alan Stern
2023-01-25 17:18 ` Paul E. McKenney
2023-01-25 17:42 ` Jonas Oberhauser
2023-01-25 19:08 ` Alan Stern
2023-01-25 19:46 ` Paul E. McKenney
2023-01-25 20:36 ` Andrea Parri
2023-01-25 21:10 ` Jonas Oberhauser
2023-01-25 21:23 ` Paul E. McKenney
2023-01-25 20:46 ` Alan Stern
2023-01-25 21:38 ` Paul E. McKenney
2023-01-25 23:33 ` Paul E. McKenney
2023-01-26 1:45 ` Alan Stern
2023-01-26 1:53 ` Paul E. McKenney
2023-01-26 12:17 ` Jonas Oberhauser
2023-01-26 18:48 ` Paul E. McKenney
2023-01-27 15:03 ` Jonas Oberhauser
2023-01-27 16:50 ` Paul E. McKenney
2023-01-27 16:54 ` Paul E. McKenney
2023-01-18 19:57 ` Jonas Oberhauser
2023-01-18 21:06 ` Paul E. McKenney
2023-01-18 2:15 ` Alan Stern
2023-01-18 5:17 ` Paul E. McKenney
2023-01-18 16:03 ` Alan Stern
2023-01-18 16:59 ` Boqun Feng
2023-01-18 17:08 ` Alan Stern
2023-01-18 17:41 ` Paul E. McKenney
2023-01-19 19:07 ` Paul E. McKenney
2023-01-14 16:55 ` Alan Stern
2023-01-14 17:35 ` Paul E. McKenney
[not found] ` <17078dd97cb6480f9c51e27058af3197@huawei.com>
2023-01-14 17:27 ` Alan Stern
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