[PATCH v4 6/6] block-copy: atomic .cancelled and .finished fields in BlockCopyCallState

[Emanuele Giuseppe Esposito <eesposit@redhat.com>]

By adding acquire/release pairs, we ensure that .ret and .error_is_read
fields are written by block_copy_dirty_clusters before .finished is true.

The atomic here are necessary because the fields are concurrently modified
also outside coroutines.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 block/block-copy.c | 33 ++++++++++++++++++---------------
 1 file changed, 18 insertions(+), 15 deletions(-)

diff --git a/block/block-copy.c b/block/block-copy.c
index 6416929abd..5348e1f61b 100644
--- a/block/block-copy.c
+++ b/block/block-copy.c
@@ -53,14 +53,14 @@ typedef struct BlockCopyCallState {
     Coroutine *co;
 
     /* State */
-    bool finished;
+    bool finished; /* atomic */
     QemuCoSleep sleep; /* TODO: protect API with a lock */
 
     /* To reference all call states from BlockCopyState */
     QLIST_ENTRY(BlockCopyCallState) list;
 
     /* OUT parameters */
-    bool cancelled;
+    bool cancelled; /* atomic */
     /* Fields protected by lock in BlockCopyState */
     bool error_is_read;
     int ret;
@@ -650,7 +650,8 @@ block_copy_dirty_clusters(BlockCopyCallState *call_state)
     assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
     assert(QEMU_IS_ALIGNED(bytes, s->cluster_size));
 
-    while (bytes && aio_task_pool_status(aio) == 0 && !call_state->cancelled) {
+    while (bytes && aio_task_pool_status(aio) == 0 &&
+           !qatomic_read(&call_state->cancelled)) {
         BlockCopyTask *task;
         int64_t status_bytes;
 
@@ -761,7 +762,7 @@ static int coroutine_fn block_copy_common(BlockCopyCallState *call_state)
     do {
         ret = block_copy_dirty_clusters(call_state);
 
-        if (ret == 0 && !call_state->cancelled) {
+        if (ret == 0 && !qatomic_read(&call_state->cancelled)) {
             WITH_QEMU_LOCK_GUARD(&s->lock) {
                 /*
                  * Check that there is no task we still need to
@@ -792,9 +793,9 @@ static int coroutine_fn block_copy_common(BlockCopyCallState *call_state)
          * 2. We have waited for some intersecting block-copy request
          *    It may have failed and produced new dirty bits.
          */
-    } while (ret > 0 && !call_state->cancelled);
+    } while (ret > 0 && !qatomic_read(&call_state->cancelled));
 
-    call_state->finished = true;
+    qatomic_store_release(&call_state->finished, true);
 
     if (call_state->cb) {
         call_state->cb(call_state->cb_opaque);
@@ -857,35 +858,37 @@ void block_copy_call_free(BlockCopyCallState *call_state)
         return;
     }
 
-    assert(call_state->finished);
+    assert(qatomic_load_acquire(&call_state->finished));
     g_free(call_state);
 }
 
 bool block_copy_call_finished(BlockCopyCallState *call_state)
 {
-    return call_state->finished;
+    return qatomic_load_acquire(&call_state->finished);
 }
 
 bool block_copy_call_succeeded(BlockCopyCallState *call_state)
 {
-    return call_state->finished && !call_state->cancelled &&
-        call_state->ret == 0;
+    return qatomic_load_acquire(&call_state->finished) &&
+           !qatomic_read(&call_state->cancelled) &&
+           call_state->ret == 0;
 }
 
 bool block_copy_call_failed(BlockCopyCallState *call_state)
 {
-    return call_state->finished && !call_state->cancelled &&
-        call_state->ret < 0;
+    return qatomic_load_acquire(&call_state->finished) &&
+           !qatomic_read(&call_state->cancelled) &&
+           call_state->ret < 0;
 }
 
 bool block_copy_call_cancelled(BlockCopyCallState *call_state)
 {
-    return call_state->cancelled;
+    return qatomic_read(&call_state->cancelled);
 }
 
 int block_copy_call_status(BlockCopyCallState *call_state, bool *error_is_read)
 {
-    assert(call_state->finished);
+    assert(qatomic_load_acquire(&call_state->finished));
     if (error_is_read) {
         *error_is_read = call_state->error_is_read;
     }
@@ -894,7 +897,7 @@ int block_copy_call_status(BlockCopyCallState *call_state, bool *error_is_read)
 
 void block_copy_call_cancel(BlockCopyCallState *call_state)
 {
-    call_state->cancelled = true;
+    qatomic_set(&call_state->cancelled, true);
     block_copy_kick(call_state);
 }
 
-- 
2.31.1