From a3f600d92da564ad35f237c8aeab268ca49377cc Mon Sep 17 00:00:00 2001 From: Alan Stern Date: Thu, 15 Nov 2018 11:20:37 -0500 Subject: [PATCH] tools/memory-model: Add SRCU support Add support for SRCU. Herd creates srcu events and linux-kernel.def associates them with three possible annotations (srcu-lock, srcu-unlock, and sync-srcu) corresponding to the API routines srcu_read_lock(), srcu_read_unlock(), and synchronize_srcu(). The linux-kernel.bell file now declares the annotations and determines matching lock/unlock pairs delimiting SRCU read-side critical sections, and it also checks for synchronize_srcu() calls inside an RCU critical section (which would generate a "sleeping in atomic context" error in real kernel code). The linux-kernel.cat file now adds SRCU-induced ordering, analogous to the existing RCU-induced ordering, to the gp and rcu-fence relations. Curiously enough, these small changes to the model's .cat code are all that is needed to describe SRCU. Portions of this patch (linux-kernel.def and the first hunk in linux-kernel.bell) were written by Luc Maranget. Signed-off-by: Alan Stern CC: Luc Maranget Signed-off-by: Paul E. McKenney Tested-by: Andrea Parri --- tools/memory-model/linux-kernel.bell | 25 +++++++++++++++++++++++++ tools/memory-model/linux-kernel.cat | 18 ++++++++++++++---- tools/memory-model/linux-kernel.def | 5 +++++ 3 files changed, 44 insertions(+), 4 deletions(-) diff --git a/tools/memory-model/linux-kernel.bell b/tools/memory-model/linux-kernel.bell index 353c8d68e030..9c42cd9ddcb4 100644 --- a/tools/memory-model/linux-kernel.bell +++ b/tools/memory-model/linux-kernel.bell @@ -33,6 +33,12 @@ enum Barriers = 'wmb (*smp_wmb*) || 'after-unlock-lock (*smp_mb__after_unlock_lock*) instructions F[Barriers] +(* SRCU *) +enum SRCU = 'srcu-lock || 'srcu-unlock || 'sync-srcu +instructions SRCU[SRCU] +(* All srcu events *) +let Srcu = Srcu-lock | Srcu-unlock | Sync-srcu + (* Compute matching pairs of nested Rcu-lock and Rcu-unlock *) let rcu-rscs = let rec unmatched-locks = Rcu-lock \ domain(matched) @@ -48,3 +54,22 @@ let rcu-rscs = let rec (* Validate nesting *) flag ~empty Rcu-lock \ domain(rcu-rscs) as unbalanced-rcu-locking flag ~empty Rcu-unlock \ range(rcu-rscs) as unbalanced-rcu-locking + +(* 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 + +(* 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 diff --git a/tools/memory-model/linux-kernel.cat b/tools/memory-model/linux-kernel.cat index b8e6197f05af..8dcb37835b61 100644 --- a/tools/memory-model/linux-kernel.cat +++ b/tools/memory-model/linux-kernel.cat @@ -33,7 +33,7 @@ let mb = ([M] ; fencerel(Mb) ; [M]) | ([M] ; po? ; [LKW] ; fencerel(After-spinlock) ; [M]) | ([M] ; po ; [UL] ; (co | po) ; [LKW] ; fencerel(After-unlock-lock) ; [M]) -let gp = po ; [Sync-rcu] ; po? +let gp = po ; [Sync-rcu | Sync-srcu] ; po? let strong-fence = mb | gp @@ -92,15 +92,18 @@ acyclic pb as propagation (* * Effects of read-side critical sections proceed from the rcu_read_unlock() - * backwards on the one hand, and from the rcu_read_lock() forwards on the - * other hand. + * 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 @@ -112,12 +115,19 @@ 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) acts as a generalized 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-fence = rcu-gp | +let rec rcu-fence = 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-fence ; rcu-link ; rcu-rscsi) | + ((srcu-gp ; rcu-link ; rcu-fence ; rcu-link ; srcu-rscsi) & loc) | (rcu-rscsi ; rcu-link ; rcu-fence ; rcu-link ; rcu-gp) | + ((srcu-rscsi ; rcu-link ; rcu-fence ; rcu-link ; srcu-gp) & loc) | (rcu-fence ; rcu-link ; rcu-fence) (* rb orders instructions just as pb does *) diff --git a/tools/memory-model/linux-kernel.def b/tools/memory-model/linux-kernel.def index b27911cc087d..1d6a120cde14 100644 --- a/tools/memory-model/linux-kernel.def +++ b/tools/memory-model/linux-kernel.def @@ -47,6 +47,11 @@ rcu_read_unlock() { __fence{rcu-unlock}; } 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); } +synchronize_srcu(X) { __srcu{sync-srcu}(X); } + // Atomic atomic_read(X) READ_ONCE(*X) atomic_set(X,V) { WRITE_ONCE(*X,V); }