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    SubjectRe: Internal vs. external barriers (was: Re: Interesting LKMM litmus test)
    On Fri, Jan 20, 2023 at 11:14:06AM -0500, Alan Stern wrote:
    > On Thu, Jan 19, 2023 at 07:55:21PM -0800, Paul E. McKenney wrote:
    > > 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.)
    >
    > Jonas is right about the reason for this. Also, his suggestion for
    > fixing the check in lock.cat makes sense.

    Very good!

    > My revised patch is below.

    Thank you! Are you OK with my putting this on a not-for-mainline branch
    for experimental purposes?

    > > https://github.com/paulmckrcu/litmus/blob/master/manual/kernel/C-srcu-nest-2.litmus
    > > https://github.com/paulmckrcu/litmus/blob/master/manual/kernel/C-srcu-nest-3.litmus
    > > https://github.com/paulmckrcu/litmus/blob/master/manual/kernel/C-srcu-nest-4.litmus
    > > https://github.com/paulmckrcu/litmus/blob/master/manual/kernel/C-srcu-nest-5.litmus
    > >
    > > All as expected.
    > >
    > > https://github.com/paulmckrcu/litmus/blob/master/manual/kernel/C-srcu-nest-6.litmus
    > >
    > > Get "Flag unbalanced-srcu-lock" and "Flag unbalanced-srcu-unlock",
    > > but this is srcu_down_read() and srcu_up_read(), where this should
    > > be OK. Ah, but I need to do the release/acquire/filter trick. Once
    > > I did that, it works as expected.
    > >
    > > https://github.com/paulmckrcu/litmus/blob/master/manual/kernel/C-srcu-nest-7.litmus
    > > https://github.com/paulmckrcu/litmus/blob/master/manual/kernel/C-srcu-nest-8.litmus
    > >
    > > Both as expected.
    > >
    > > Getting there!!!
    >
    > Good news.

    And all of the litmus-repo tests up to ten processes passed. Woo-hoo!!!

    Thanx, Paul

    > 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 +53,31 @@ 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 carry-srcu-data = (data ; [~ Srcu-unlock] ; rf)*
    > +let srcu-rscs = ([Srcu-lock] ; carry-srcu-data ; data ; [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); }
    >
    > Index: usb-devel/tools/memory-model/lock.cat
    > ===================================================================
    > --- usb-devel.orig/tools/memory-model/lock.cat
    > +++ usb-devel/tools/memory-model/lock.cat
    > @@ -36,9 +36,9 @@ let RU = try RU with emptyset
    > (* Treat RL as a kind of LF: a read with no ordering properties *)
    > let LF = LF | RL
    >
    > -(* There should be no ordinary R or W accesses to spinlocks *)
    > -let ALL-LOCKS = LKR | LKW | UL | LF | RU
    > -flag ~empty [M \ IW] ; loc ; [ALL-LOCKS] as mixed-lock-accesses
    > +(* There should be no ordinary R or W accesses to spinlocks or SRCU structs *)
    > +let ALL-LOCKS = LKR | LKW | UL | LF | RU | Srcu-lock | Srcu-unlock | Sync-srcu
    > +flag ~empty [M \ IW \ ALL-LOCKS] ; loc ; [ALL-LOCKS] as mixed-lock-accesses
    >
    > (* Link Lock-Reads to their RMW-partner Lock-Writes *)
    > let lk-rmw = ([LKR] ; po-loc ; [LKW]) \ (po ; po)

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