Read/write concurrency of pvector library is implemented by a temp vector
and RCU protection. Considering performance reason, insertion does not
follow this scheme.
In insertion function, a thread fence ensures size incrementation is done
after new entry is stored. But there is no barrier in the iteration
fuction(pvector_cursor_init). Entry point access may be reorderd before
loading vector size, so the invalid entry point may be loaded when vector
iteration.
This patch fixes it by acquire-release pair. It can guarantee new size is
observed by reader after new entry stored by writer. And this is
implemented by one-way barrier instead of two-way memory fence.
Reviewed-by: Gavin Hu <gavin...@arm.com>
Reviewed-by: Lijian Zhang <lijian.zh...@arm.com>
Signed-off-by: Yanqin Wei <yanqin....@arm.com>
---
lib/pvector.c | 16 +++++++++-------
lib/pvector.h | 10 ++++++----
2 files changed, 15 insertions(+), 11 deletions(-)
diff --git a/lib/pvector.c b/lib/pvector.c
index aaeee9214..d367079fd 100644
--- a/lib/pvector.c
+++ b/lib/pvector.c
@@ -33,7 +33,7 @@ pvector_impl_alloc(size_t size)
struct pvector_impl *impl;
impl = xmalloc(sizeof *impl + size * sizeof impl->vector[0]);
- impl->size = 0;
+ atomic_init(&impl->size, 0);
impl->allocated = size;
return impl;
@@ -117,18 +117,20 @@ pvector_insert(struct pvector *pvec, void *ptr, int
priority)
{
struct pvector_impl *temp = pvec->temp;
struct pvector_impl *old = pvector_impl_get(pvec);
+ size_t size;
ovs_assert(ptr != NULL);
+ atomic_read_relaxed(&old->size, &size);
+
/* Check if can add to the end without reallocation. */
- if (!temp && old->allocated > old->size &&
- (!old->size || priority <= old->vector[old->size - 1].priority)) {
- old->vector[old->size].ptr = ptr;
- old->vector[old->size].priority = priority;
+ if (!temp && old->allocated > size &&
+ (!size || priority <= old->vector[size - 1].priority)) {
+ old->vector[size].ptr = ptr;
+ old->vector[size].priority = priority;
/* Size increment must not be visible to the readers before the new
* entry is stored. */
- atomic_thread_fence(memory_order_release);
- ++old->size;
+ atomic_store_explicit(&old->size, size + 1, memory_order_release);
} else {
if (!temp) {
temp = pvector_impl_dup(old);
diff --git a/lib/pvector.h b/lib/pvector.h
index b990ed9d5..c65276638 100644
--- a/lib/pvector.h
+++ b/lib/pvector.h
@@ -69,8 +69,8 @@ struct pvector_entry {
};
struct pvector_impl {
- size_t size; /* Number of entries in the vector. */
- size_t allocated; /* Number of allocated entries. */
+ atomic_size_t size; /* Number of entries in the vector. */
+ size_t allocated; /* Number of allocated entries. */
struct pvector_entry vector[];
};
@@ -181,12 +181,14 @@ pvector_cursor_init(const struct pvector *pvec,
{
const struct pvector_impl *impl;
struct pvector_cursor cursor;
+ size_t size;
impl = ovsrcu_get(struct pvector_impl *, &pvec->impl);
- ovs_prefetch_range(impl->vector, impl->size * sizeof impl->vector[0]);
+ atomic_read_explicit(&impl->size, &size, memory_order_acquire);
+ ovs_prefetch_range(impl->vector, size * sizeof impl->vector[0]);
- cursor.size = impl->size;
+ cursor.size = size;
cursor.vector = impl->vector;
cursor.entry_idx = -1;
--
2.17.1
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