// SPDX-License-Identifier: GPL-2.0+
(*
* Copyright (C) 2015 Jade Alglave <[email protected]>,
* Copyright (C) 2016 Luc Maranget <[email protected]> for Inria
* Copyright (C) 2017 Alan Stern <[email protected]>,
* Andrea Parri <[email protected]>
*
* An earlier version of this file appeared in the companion webpage for
* "Frightening small children and disconcerting grown-ups: Concurrency
* in the Linux kernel" by Alglave, Maranget, McKenney, Parri, and Stern,
* which appeared in ASPLOS 2018.
*)
"Linux-kernel memory consistency model"
(*
* File "lock.cat" handles locks and is experimental.
* It can be replaced by include "cos.cat" for tests that do not use locks.
*)
include "lock.cat"
(*******************)
(* Basic relations *)
(*******************)
(* Release Acquire *)
let acq-po = [Acquire] ; po ; [M]
let po-rel = [M] ; po ; [Release]
let po-unlock-lock-po = po ; [UL] ; (po|rf) ; [LKR] ; po
(* Fences *)
let R4rmb = R \ Noreturn (* Reads for which rmb works *)
let rmb = [R4rmb] ; fencerel(Rmb) ; [R4rmb]
let wmb = [W] ; fencerel(Wmb) ; [W]
let mb = ([M] ; fencerel(Mb) ; [M]) |
([M] ; fencerel(Before-atomic) ; [RMW] ; po? ; [M]) |
([M] ; po? ; [RMW] ; fencerel(After-atomic) ; [M]) |
([M] ; po? ; [LKW] ; fencerel(After-spinlock) ; [M]) |
(*
* Note: The po-unlock-lock-po relation only passes the lock to the direct
* successor, perhaps giving the impression that the ordering of the
* smp_mb__after_unlock_lock() fence only affects a single lock handover.
* However, in a longer sequence of lock handovers, the implicit
* A-cumulative release fences of lock-release ensure that any stores that
* propagate to one of the involved CPUs before it hands over the lock to
* the next CPU will also propagate to the final CPU handing over the lock
* to the CPU that executes the fence. Therefore, all those stores are
* also affected by the fence.
*)
([M] ; po-unlock-lock-po ;
[After-unlock-lock] ; po ; [M]) |
([M] ; po? ; [Srcu-unlock] ; fencerel(After-srcu-read-unlock) ; [M])
let gp = po ; [Sync-rcu | Sync-srcu] ; po?
let strong-fence = mb | gp
let nonrw-fence = strong-fence | po-rel | acq-po
let fence = nonrw-fence | wmb | rmb
let barrier = fencerel(Barrier | Rmb | Wmb | Mb | Sync-rcu | Sync-srcu |
Before-atomic | After-atomic | Acquire | Release |
Rcu-lock | Rcu-unlock | Srcu-lock | Srcu-unlock) |
(po ; [Release]) | ([Acquire] ; po)
(**********************************)
(* Fundamental coherence ordering *)
(**********************************)
(* Sequential Consistency Per Variable *)
let com = rf | co | fr
acyclic po-loc | com as coherence
(* Atomic Read-Modify-Write *)
empty rmw & (fre ; coe) as atomic
(**********************************)
(* Instruction execution ordering *)
(**********************************)
(* Preserved Program Order *)
let dep = addr | data
let rwdep = (dep | ctrl) ; [W]
let overwrite = co | fr
let to-w = rwdep | (overwrite & int) | (addr ; [Plain] ; wmb)
let to-r = (addr ; [R]) | (dep ; [Marked] ; rfi)
let ppo = to-r | to-w | (fence & int) | (po-unlock-lock-po & int)
(* Propagation: Ordering from release operations and strong fences. *)
let A-cumul(r) = (rfe ; [Marked])? ; r
let rmw-sequence = (rf ; rmw)*
let cumul-fence = [Marked] ; (A-cumul(strong-fence | po-rel) | wmb |
po-unlock-lock-po) ; [Marked] ; rmw-sequence
let prop = [Marked] ; (overwrite & ext)? ; cumul-fence* ;
[Marked] ; rfe? ; [Marked]
(*
* Happens Before: Ordering from the passage of time.
* No fences needed here for prop because relation confined to one process.
*)
let hb = [Marked] ; (ppo | rfe | ((prop \ id) & int)) ; [Marked]
acyclic hb as happens-before
(****************************************)
(* Write and fence propagation ordering *)
(****************************************)
(* Propagation: Each non-rf link needs a strong fence. *)
let pb = prop ; strong-fence ; hb* ; [Marked]
acyclic pb as propagation
(*******)
(* RCU *)
(*******)
(*
* Effects of read-side critical sections proceed from the rcu_read_unlock()
* or srcu_read_unlock() backwards on the one hand, and from the
* rcu_read_lock() or srcu_read_lock() forwards on the other hand.
*
* In the definition of rcu-fence below, the po term at the left-hand side
* of each disjunct and the po? term at the right-hand end have been factored
* out. They have been moved into the definitions of rcu-link and rb.
* This was necessary in order to apply the "& loc" tests correctly.
*)
let rcu-gp = [Sync-rcu] (* Compare with gp *)
let srcu-gp = [Sync-srcu]
let rcu-rscsi = rcu-rscs^-1
let srcu-rscsi = srcu-rscs^-1
(*
* The synchronize_rcu() strong fence is special in that it can order not
* one but two non-rf relations, but only in conjunction with an RCU
* read-side critical section.
*)
let rcu-link = po? ; hb* ; pb* ; prop ; po
(*
* Any sequence containing at least as many grace periods as RCU read-side
* critical sections (joined by rcu-link) induces order like a generalized
* inter-CPU strong fence.
* Likewise for SRCU grace periods and read-side critical sections, provided
* the synchronize_srcu() and srcu_read_[un]lock() calls refer to the same
* struct srcu_struct location.
*)
let rec rcu-order = rcu-gp | srcu-gp |
(rcu-gp ; rcu-link ; rcu-rscsi) |
((srcu-gp ; rcu-link ; srcu-rscsi) & loc) |
(rcu-rscsi ; rcu-link ; rcu-gp) |
((srcu-rscsi ; rcu-link ; srcu-gp) & loc) |
(rcu-gp ; rcu-link ; rcu-order ; rcu-link ; rcu-rscsi) |
((srcu-gp ; rcu-link ; rcu-order ; rcu-link ; srcu-rscsi) & loc) |
(rcu-rscsi ; rcu-link ; rcu-order ; rcu-link ; rcu-gp) |
((srcu-rscsi ; rcu-link ; rcu-order ; rcu-link ; srcu-gp) & loc) |
(rcu-order ; rcu-link ; rcu-order)
let rcu-fence = po ; rcu-order ; po?
let fence = fence | rcu-fence
let strong-fence = strong-fence | rcu-fence
(* rb orders instructions just as pb does *)
let rb = prop ; rcu-fence ; hb* ; pb* ; [Marked]
irreflexive rb as rcu
(*
* The happens-before, propagation, and rcu constraints are all
* expressions of temporal ordering. They could be replaced by
* a single constraint on an "executes-before" relation, xb:
*
* let xb = hb | pb | rb
* acyclic xb as executes-before
*)
(*********************************)
(* Plain accesses and data races *)
(*********************************)
(* Warn about plain writes and marked accesses in the same region *)
let mixed-accesses = ([Plain & W] ; (po-loc \ barrier) ; [Marked]) |
([Marked] ; (po-loc \ barrier) ; [Plain & W])
flag ~empty mixed-accesses as mixed-accesses
(* Executes-before and visibility *)
let xbstar = (hb | pb | rb)*
let vis = cumul-fence* ; rfe? ; [Marked] ;
((strong-fence ; [Marked] ; xbstar) | (xbstar & int))
(* Boundaries for lifetimes of plain accesses *)
let w-pre-bounded = [Marked] ; (addr | fence)?
let r-pre-bounded = [Marked] ; (addr | nonrw-fence |
([R4rmb] ; fencerel(Rmb) ; [~Noreturn]))?
let w-post-bounded = fence? ; [Marked] ; rmw-sequence
let r-post-bounded = (nonrw-fence | ([~Noreturn] ; fencerel(Rmb) ; [R4rmb]))? ;
[Marked]
(* Visibility and executes-before for plain accesses *)
let ww-vis = fence | (strong-fence ; xbstar ; w-pre-bounded) |
(w-post-bounded ; vis ; w-pre-bounded)
let wr-vis = fence | (strong-fence ; xbstar ; r-pre-bounded) |
(w-post-bounded ; vis ; r-pre-bounded)
let rw-xbstar = fence | (r-post-bounded ; xbstar ; w-pre-bounded)
(* Potential races *)
let pre-race = ext & ((Plain * M) | ((M \ IW) * Plain))
(* Coherence requirements for plain accesses *)
let wr-incoh = pre-race & rf & rw-xbstar^-1
let rw-incoh = pre-race & fr & wr-vis^-1
let ww-incoh = pre-race & co & ww-vis^-1
empty (wr-incoh | rw-incoh | ww-incoh) as plain-coherence
(* Actual races *)
let ww-nonrace = ww-vis & ((Marked * W) | rw-xbstar) & ((W * Marked) | wr-vis)
let ww-race = (pre-race & co) \ ww-nonrace
let wr-race = (pre-race & (co? ; rf)) \ wr-vis \ rw-xbstar^-1
let rw-race = (pre-race & fr) \ rw-xbstar
flag ~empty (ww-race | wr-race | rw-race) as data-race
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