| Message ID | 1453740558-16303-5-git-send-email-alex.bennee@linaro.org |
|---|---|
| State | New |
| Headers | show |
On 25/01/2016 17:49, Alex Bennée wrote: > After building with the ThreadSanitizer I ran make check and started > going through the failures reported. Most are failures to use atomic > primitives to access variables previously atomically set. While this > likely will work on x86 it could cause problems on other architectures. It will work on other architectures, because there are memory barriers (either explicit, or implicit in other atomic_* ops). In fact, using atomic_read/atomic_set would actually fix bugs in x86 :) if it weren't for commit 3bbf572 ("atomics: add explicit compiler fence in __atomic memory barriers", 2015-06-03). > - async: use atomic reads for scheduled/notify_me > - thread-pool: use atomic_mb_read/set to for thread ->state Please use atomic_read/atomic_set and keep the memory barriers. That's a fine way to convert code that uses non-atomic accesses together with memory barriers (not just thread-pool, also e.g. virtio). Otherwise looks sane, thanks! Paolo > - test-thread-pool: use atomic read for data.n > > Signed-off-by: Alex Bennée <alex.bennee@linaro.org> > --- > async.c | 4 ++-- > tests/test-thread-pool.c | 2 +- > thread-pool.c | 9 ++++----- > 3 files changed, 7 insertions(+), 8 deletions(-) > > diff --git a/async.c b/async.c > index e106072..8d5f810 100644 > --- a/async.c > +++ b/async.c > @@ -165,7 +165,7 @@ aio_compute_timeout(AioContext *ctx) > QEMUBH *bh; > > for (bh = ctx->first_bh; bh; bh = bh->next) { > - if (!bh->deleted && bh->scheduled) { > + if (!bh->deleted && atomic_read(&bh->scheduled)) { > if (bh->idle) { > /* idle bottom halves will be polled at least > * every 10ms */ > @@ -286,7 +286,7 @@ void aio_notify(AioContext *ctx) > * with atomic_or in aio_ctx_prepare or atomic_add in aio_poll. > */ > smp_mb(); > - if (ctx->notify_me) { > + if (atomic_read(&ctx->notify_me)) { > event_notifier_set(&ctx->notifier); > atomic_mb_set(&ctx->notified, true); > } > diff --git a/tests/test-thread-pool.c b/tests/test-thread-pool.c > index ccdee39..5694ad9 100644 > --- a/tests/test-thread-pool.c > +++ b/tests/test-thread-pool.c > @@ -46,7 +46,7 @@ static void test_submit(void) > { > WorkerTestData data = { .n = 0 }; > thread_pool_submit(pool, worker_cb, &data); > - while (data.n == 0) { > + while (atomic_read(&data.n) == 0) { > aio_poll(ctx, true); > } > g_assert_cmpint(data.n, ==, 1); > diff --git a/thread-pool.c b/thread-pool.c > index 402c778..97b2c0c 100644 > --- a/thread-pool.c > +++ b/thread-pool.c > @@ -99,15 +99,14 @@ static void *worker_thread(void *opaque) > > req = QTAILQ_FIRST(&pool->request_list); > QTAILQ_REMOVE(&pool->request_list, req, reqs); > - req->state = THREAD_ACTIVE; > + atomic_mb_set(&req->state, THREAD_ACTIVE); > qemu_mutex_unlock(&pool->lock); > > ret = req->func(req->arg); > > req->ret = ret; > /* Write ret before state. */ > - smp_wmb(); > - req->state = THREAD_DONE; > + atomic_mb_set(&req->state, THREAD_DONE); > > qemu_mutex_lock(&pool->lock); > > @@ -167,7 +166,7 @@ static void thread_pool_completion_bh(void *opaque) > > restart: > QLIST_FOREACH_SAFE(elem, &pool->head, all, next) { > - if (elem->state != THREAD_DONE) { > + if (atomic_read(&elem->state) != THREAD_DONE) { > continue; > } > > @@ -201,7 +200,7 @@ static void thread_pool_cancel(BlockAIOCB *acb) > trace_thread_pool_cancel(elem, elem->common.opaque); > > qemu_mutex_lock(&pool->lock); > - if (elem->state == THREAD_QUEUED && > + if (atomic_mb_read(&elem->state) == THREAD_QUEUED && > /* No thread has yet started working on elem. we can try to "steal" > * the item from the worker if we can get a signal from the > * semaphore. Because this is non-blocking, we can do it with >
diff --git a/async.c b/async.c index e106072..8d5f810 100644 --- a/async.c +++ b/async.c @@ -165,7 +165,7 @@ aio_compute_timeout(AioContext *ctx) QEMUBH *bh; for (bh = ctx->first_bh; bh; bh = bh->next) { - if (!bh->deleted && bh->scheduled) { + if (!bh->deleted && atomic_read(&bh->scheduled)) { if (bh->idle) { /* idle bottom halves will be polled at least * every 10ms */ @@ -286,7 +286,7 @@ void aio_notify(AioContext *ctx) * with atomic_or in aio_ctx_prepare or atomic_add in aio_poll. */ smp_mb(); - if (ctx->notify_me) { + if (atomic_read(&ctx->notify_me)) { event_notifier_set(&ctx->notifier); atomic_mb_set(&ctx->notified, true); } diff --git a/tests/test-thread-pool.c b/tests/test-thread-pool.c index ccdee39..5694ad9 100644 --- a/tests/test-thread-pool.c +++ b/tests/test-thread-pool.c @@ -46,7 +46,7 @@ static void test_submit(void) { WorkerTestData data = { .n = 0 }; thread_pool_submit(pool, worker_cb, &data); - while (data.n == 0) { + while (atomic_read(&data.n) == 0) { aio_poll(ctx, true); } g_assert_cmpint(data.n, ==, 1); diff --git a/thread-pool.c b/thread-pool.c index 402c778..97b2c0c 100644 --- a/thread-pool.c +++ b/thread-pool.c @@ -99,15 +99,14 @@ static void *worker_thread(void *opaque) req = QTAILQ_FIRST(&pool->request_list); QTAILQ_REMOVE(&pool->request_list, req, reqs); - req->state = THREAD_ACTIVE; + atomic_mb_set(&req->state, THREAD_ACTIVE); qemu_mutex_unlock(&pool->lock); ret = req->func(req->arg); req->ret = ret; /* Write ret before state. */ - smp_wmb(); - req->state = THREAD_DONE; + atomic_mb_set(&req->state, THREAD_DONE); qemu_mutex_lock(&pool->lock); @@ -167,7 +166,7 @@ static void thread_pool_completion_bh(void *opaque) restart: QLIST_FOREACH_SAFE(elem, &pool->head, all, next) { - if (elem->state != THREAD_DONE) { + if (atomic_read(&elem->state) != THREAD_DONE) { continue; } @@ -201,7 +200,7 @@ static void thread_pool_cancel(BlockAIOCB *acb) trace_thread_pool_cancel(elem, elem->common.opaque); qemu_mutex_lock(&pool->lock); - if (elem->state == THREAD_QUEUED && + if (atomic_mb_read(&elem->state) == THREAD_QUEUED && /* No thread has yet started working on elem. we can try to "steal" * the item from the worker if we can get a signal from the * semaphore. Because this is non-blocking, we can do it with
After building with the ThreadSanitizer I ran make check and started going through the failures reported. Most are failures to use atomic primitives to access variables previously atomically set. While this likely will work on x86 it could cause problems on other architectures. - async: use atomic reads for scheduled/notify_me - thread-pool: use atomic_mb_read/set to for thread ->state - test-thread-pool: use atomic read for data.n Signed-off-by: Alex Bennée <alex.bennee@linaro.org> --- async.c | 4 ++-- tests/test-thread-pool.c | 2 +- thread-pool.c | 9 ++++----- 3 files changed, 7 insertions(+), 8 deletions(-)