This commit adds support for smp_mb__after_srcu_read_unlock(), which, when combined with a prior srcu_read_unlock(), implies a full memory barrier. No ordering is guaranteed to accesses between the two, and placing accesses between is bad practice in any case. Tests may be found at https://github.com/paulmckrcu/litmus in files matching manual/kernel/C-srcu-mb-*.litmus. If we really do figure a way to weaken srcu_read_unlock() to release semantics, this functionality might play a greater role. It can be argued that smp_mb__after_srcu_read_unlock() should instead be smp_mb__before_srcu_read_unlock() to make it more clear that the full memory barrier precedes the end of any ongoing grace period. There are not that many uses of smp_mb__after_srcu_read_unlock(), so... Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> diff --git a/tools/memory-model/linux-kernel.bell b/tools/memory-model/linux-kernel.bell index dc464854d28a4..b92fdf7f6eeb1 100644 --- a/tools/memory-model/linux-kernel.bell +++ b/tools/memory-model/linux-kernel.bell @@ -31,7 +31,8 @@ enum Barriers = 'wmb (*smp_wmb*) || 'before-atomic (*smp_mb__before_atomic*) || 'after-atomic (*smp_mb__after_atomic*) || 'after-spinlock (*smp_mb__after_spinlock*) || - 'after-unlock-lock (*smp_mb__after_unlock_lock*) + 'after-unlock-lock (*smp_mb__after_unlock_lock*) || + 'after-srcu-read-unlock (*smp_mb__after_srcu_read_unlock*) instructions F[Barriers] (* SRCU *) diff --git a/tools/memory-model/linux-kernel.cat b/tools/memory-model/linux-kernel.cat index 6e531457bb738..3a4d3b49e85cb 100644 --- a/tools/memory-model/linux-kernel.cat +++ b/tools/memory-model/linux-kernel.cat @@ -49,7 +49,8 @@ let mb = ([M] ; fencerel(Mb) ; [M]) | * also affected by the fence. *) ([M] ; po-unlock-lock-po ; - [After-unlock-lock] ; po ; [M]) + [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 diff --git a/tools/memory-model/linux-kernel.def b/tools/memory-model/linux-kernel.def index ef0f3c1850dee..a6b6fbc9d0b24 100644 --- a/tools/memory-model/linux-kernel.def +++ b/tools/memory-model/linux-kernel.def @@ -24,6 +24,7 @@ smp_mb__before_atomic() { __fence{before-atomic}; } smp_mb__after_atomic() { __fence{after-atomic}; } smp_mb__after_spinlock() { __fence{after-spinlock}; } smp_mb__after_unlock_lock() { __fence{after-unlock-lock}; } +smp_mb__after_srcu_read_unlock() { __fence{after-srcu-read-unlock}; } barrier() { __fence{barrier}; } // Exchange
