From b393e8b33efd2ee08576ceddc10c2b4bfb3b5435 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 9 Oct 2017 10:20:44 -0700 Subject: percpu: READ_ONCE() now implies smp_read_barrier_depends() Because READ_ONCE() now implies smp_read_barrier_depends(), this commit removes the now-redundant smp_read_barrier_depends() following the READ_ONCE() in __ref_is_percpu(). Signed-off-by: Paul E. McKenney Acked-by: Tejun Heo Cc: Christoph Lameter --- lib/percpu-refcount.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'lib') diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c index fe03c6d52761..30e7dd88148b 100644 --- a/lib/percpu-refcount.c +++ b/lib/percpu-refcount.c @@ -197,10 +197,10 @@ static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref) atomic_long_add(PERCPU_COUNT_BIAS, &ref->count); /* - * Restore per-cpu operation. smp_store_release() is paired with - * smp_read_barrier_depends() in __ref_is_percpu() and guarantees - * that the zeroing is visible to all percpu accesses which can see - * the following __PERCPU_REF_ATOMIC clearing. + * Restore per-cpu operation. smp_store_release() is paired + * with READ_ONCE() in __ref_is_percpu() and guarantees that the + * zeroing is visible to all percpu accesses which can see the + * following __PERCPU_REF_ATOMIC clearing. */ for_each_possible_cpu(cpu) *per_cpu_ptr(percpu_count, cpu) = 0; -- cgit v1.2.3-70-g09d2 From 516df050615e4b0fd2dd0448cb5a807208a3837a Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 9 Oct 2017 11:39:57 -0700 Subject: lib/assoc_array: Remove smp_read_barrier_depends() Now that smp_read_barrier_depends() is implied by READ_ONCE(), the several smp_read_barrier_depends() calls may be removed from lib/assoc_array.c. This commit makes this change and marks the READ_ONCE() calls that head address dependencies. Signed-off-by: Paul E. McKenney Cc: Jonathan Corbet Cc: Mark Rutland Cc: Alexander Kuleshov Cc: David Howells --- lib/assoc_array.c | 37 ++++++++++++------------------------- 1 file changed, 12 insertions(+), 25 deletions(-) (limited to 'lib') diff --git a/lib/assoc_array.c b/lib/assoc_array.c index b77d51da8c73..c6659cb37033 100644 --- a/lib/assoc_array.c +++ b/lib/assoc_array.c @@ -38,12 +38,10 @@ begin_node: if (assoc_array_ptr_is_shortcut(cursor)) { /* Descend through a shortcut */ shortcut = assoc_array_ptr_to_shortcut(cursor); - smp_read_barrier_depends(); - cursor = READ_ONCE(shortcut->next_node); + cursor = READ_ONCE(shortcut->next_node); /* Address dependency. */ } node = assoc_array_ptr_to_node(cursor); - smp_read_barrier_depends(); slot = 0; /* We perform two passes of each node. @@ -55,15 +53,12 @@ begin_node: */ has_meta = 0; for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) { - ptr = READ_ONCE(node->slots[slot]); + ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */ has_meta |= (unsigned long)ptr; if (ptr && assoc_array_ptr_is_leaf(ptr)) { - /* We need a barrier between the read of the pointer - * and dereferencing the pointer - but only if we are - * actually going to dereference it. + /* We need a barrier between the read of the pointer, + * which is supplied by the above READ_ONCE(). */ - smp_read_barrier_depends(); - /* Invoke the callback */ ret = iterator(assoc_array_ptr_to_leaf(ptr), iterator_data); @@ -86,10 +81,8 @@ begin_node: continue_node: node = assoc_array_ptr_to_node(cursor); - smp_read_barrier_depends(); - for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) { - ptr = READ_ONCE(node->slots[slot]); + ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */ if (assoc_array_ptr_is_meta(ptr)) { cursor = ptr; goto begin_node; @@ -98,16 +91,15 @@ continue_node: finished_node: /* Move up to the parent (may need to skip back over a shortcut) */ - parent = READ_ONCE(node->back_pointer); + parent = READ_ONCE(node->back_pointer); /* Address dependency. */ slot = node->parent_slot; if (parent == stop) return 0; if (assoc_array_ptr_is_shortcut(parent)) { shortcut = assoc_array_ptr_to_shortcut(parent); - smp_read_barrier_depends(); cursor = parent; - parent = READ_ONCE(shortcut->back_pointer); + parent = READ_ONCE(shortcut->back_pointer); /* Address dependency. */ slot = shortcut->parent_slot; if (parent == stop) return 0; @@ -147,7 +139,7 @@ int assoc_array_iterate(const struct assoc_array *array, void *iterator_data), void *iterator_data) { - struct assoc_array_ptr *root = READ_ONCE(array->root); + struct assoc_array_ptr *root = READ_ONCE(array->root); /* Address dependency. */ if (!root) return 0; @@ -194,7 +186,7 @@ assoc_array_walk(const struct assoc_array *array, pr_devel("-->%s()\n", __func__); - cursor = READ_ONCE(array->root); + cursor = READ_ONCE(array->root); /* Address dependency. */ if (!cursor) return assoc_array_walk_tree_empty; @@ -216,11 +208,9 @@ jumped: consider_node: node = assoc_array_ptr_to_node(cursor); - smp_read_barrier_depends(); - slot = segments >> (level & ASSOC_ARRAY_KEY_CHUNK_MASK); slot &= ASSOC_ARRAY_FAN_MASK; - ptr = READ_ONCE(node->slots[slot]); + ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */ pr_devel("consider slot %x [ix=%d type=%lu]\n", slot, level, (unsigned long)ptr & 3); @@ -254,7 +244,6 @@ consider_node: cursor = ptr; follow_shortcut: shortcut = assoc_array_ptr_to_shortcut(cursor); - smp_read_barrier_depends(); pr_devel("shortcut to %d\n", shortcut->skip_to_level); sc_level = level + ASSOC_ARRAY_LEVEL_STEP; BUG_ON(sc_level > shortcut->skip_to_level); @@ -294,7 +283,7 @@ follow_shortcut: } while (sc_level < shortcut->skip_to_level); /* The shortcut matches the leaf's index to this point. */ - cursor = READ_ONCE(shortcut->next_node); + cursor = READ_ONCE(shortcut->next_node); /* Address dependency. */ if (((level ^ sc_level) & ~ASSOC_ARRAY_KEY_CHUNK_MASK) != 0) { level = sc_level; goto jumped; @@ -331,20 +320,18 @@ void *assoc_array_find(const struct assoc_array *array, return NULL; node = result.terminal_node.node; - smp_read_barrier_depends(); /* If the target key is available to us, it's has to be pointed to by * the terminal node. */ for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) { - ptr = READ_ONCE(node->slots[slot]); + ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */ if (ptr && assoc_array_ptr_is_leaf(ptr)) { /* We need a barrier between the read of the pointer * and dereferencing the pointer - but only if we are * actually going to dereference it. */ leaf = assoc_array_ptr_to_leaf(ptr); - smp_read_barrier_depends(); if (ops->compare_object(leaf, index_key)) return (void *)leaf; } -- cgit v1.2.3-70-g09d2