Messages in this thread |  | | Date | Sun, 15 Jan 2023 20:23:29 -0800 | From | "Paul E. McKenney" <> | Subject | Re: Internal vs. external barriers (was: Re: Interesting LKMM litmus test) |
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On Sun, Jan 15, 2023 at 03:46:10PM -0500, Alan Stern wrote: > On Sun, Jan 15, 2023 at 10:10:52AM -0800, Paul E. McKenney wrote: > > On Sun, Jan 15, 2023 at 11:23:31AM -0500, Alan Stern wrote: > > > On Sat, Jan 14, 2023 at 09:15:10PM -0800, Paul E. McKenney wrote: > > > > What am I missing here? > > > > > > I don't think you're missing anything. This is a matter for Boqun or > > > Luc; it must have something to do with the way herd treats the > > > srcu_read_lock() and srcu_read_unlock() primitives. > > > > It looks like we need something that tracks (data | rf)* between > > the return value of srcu_read_lock() and the second parameter of > > srcu_read_unlock(). The reason for rf rather than rfi is the upcoming > > srcu_down_read() and srcu_up_read(). > > Or just make herd treat srcu_read_lock(s) as an annotated equivalent of > READ_ONCE(&s) and srcu_read_unlock(s, v) as an annotated equivalent of > WRITE_ONCE(s, v). But with some special accomodation to avoid > interaction with the new carry-dep relation.
This is a modification to herd7 you are suggesting? Otherwise, I am suffering a failure of imagination on how to properly sort it from the other READ_ONCE() and WRITE_ONCE() instances.
> > But what I will do in the meantime is to switch back to a commit that > > simply flags nesting of same-srcu_struct SRCU read-side critical sections, > > while blindly assuming that the return value of a given srcu_read_lock() > > is passed in to the corresponding srcu_read_unlock(): > > > > ------------------------------------------------------------------------ > > > > (* Compute matching pairs of Srcu-lock and Srcu-unlock, but prohibit nesting *) > > let srcu-unmatched = Srcu-lock | Srcu-unlock > > let srcu-unmatched-po = ([srcu-unmatched] ; po ; [srcu-unmatched]) & loc > > let srcu-unmatched-locks-to-unlock = ([Srcu-lock] ; po ; [Srcu-unlock]) & loc > > let srcu-rscs = srcu-unmatched-locks-to-unlock \ (srcu-unmatched-po ; srcu-unmatched-po) > > > > (* Validate nesting *) > > flag ~empty Srcu-lock \ domain(srcu-rscs) as unbalanced-srcu-locking > > flag ~empty Srcu-unlock \ range(srcu-rscs) as unbalanced-srcu-locking > > > > (* 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 > > > > ------------------------------------------------------------------------ > > > > Or is there some better intermediate position that could be taken? > > Do you mean go back to the current linux-kernel.bell? The code you > wrote above is different, since it prohibits nesting.
Not to the current linux-kernel.bell, but, as you say, making the change to obtain a better approximation by prohibiting nesting.
Thanx, Paul
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