Messages in this thread |  | | Date | Sun, 15 Jan 2023 10:10:52 -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 11:23:31AM -0500, Alan Stern wrote: > On Sat, Jan 14, 2023 at 09:15:10PM -0800, Paul E. McKenney wrote: > > On Sat, Jan 14, 2023 at 03:19:06PM -0500, Alan Stern wrote: > > > On Sat, Jan 14, 2023 at 10:15:37AM -0800, Paul E. McKenney wrote: > > > > Nevertheless, here is the resulting .bell fragment: > > > > > > > > ------------------------------------------------------------------------ > > > > > > > > (* Compute matching pairs of Srcu-lock and Srcu-unlock *) > > > > let srcu-rscs = ([Srcu-lock] ; 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 > > > > > > > > (* 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 > > > > > > I forgot to mention... An appropriate check for one srcu_read_lock() > > > matched to more than one srcu_read_unlock() would be something like > > > this: > > > > > > flag ~empty (srcu-rscs^-1 ; srcu-rscs) \ id as multiple-unlocks > > > > I have added this, thank you! > > > > > Alan > > > > > > PS: Do you agree that we should change the names of the first two flags > > > above to unbalanced-srcu-lock and unbalanced-srcu-unlock, respectively > > > (and similarly for the rcu checks)? It might help to be a little more > > > specific about how the locking is wrong when we detect an error. > > > > I have made this change, again, thank you! > > > > But I also added this: > > > > flag empty srcu-rscs as no-srcu-readers > > > > And it is always flagged. So far, I have not found any sort of relation > > that connects Srcu-lock to Srcu-unlock other than po. I tried data, > > ctrl, addr, rf, rfi, and combinations thereof. > > > > 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().
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():
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(* 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?
Thanx, Paul
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