qcow2: Take locks for accessing bs->file

[mirror_qemu.git] / block / graph-lock.c

diff --git a/block/graph-lock.c b/block/graph-lock.c
index a92c6ae219ea41a827916a2bf44c964167b2d8d0..e5525ee2db4474c70a68a70be81edd2efa23d0c6 100644 (file)
--- a/block/graph-lock.c
+++ b/block/graph-lock.c
@@ -30,10 +30,8 @@ BdrvGraphLock graph_lock;
 /* Protects the list of aiocontext and orphaned_reader_count */
 static QemuMutex aio_context_list_lock;
 
-#if 0
 /* Written and read with atomic operations. */
 static int has_writer;
-#endif
 
 /*
  * A reader coroutine could move from an AioContext to another.
@@ -90,7 +88,6 @@ void unregister_aiocontext(AioContext *ctx)
     g_free(ctx->bdrv_graph);
 }
 
-#if 0
 static uint32_t reader_count(void)
 {
     BdrvGraphRWlock *brdv_graph;
@@ -98,7 +95,7 @@ static uint32_t reader_count(void)
 
     QEMU_LOCK_GUARD(&aio_context_list_lock);
 
-    /* rd can temporarly be negative, but the total will *always* be >= 0 */
+    /* rd can temporarily be negative, but the total will *always* be >= 0 */
     rd = orphaned_reader_count;
     QTAILQ_FOREACH(brdv_graph, &aio_context_list, next_aio) {
         rd += qatomic_read(&brdv_graph->reader_count);
@@ -108,18 +105,27 @@ static uint32_t reader_count(void)
     assert((int32_t)rd >= 0);
     return rd;
 }
-#endif
 
-void bdrv_graph_wrlock(void)
+void no_coroutine_fn bdrv_graph_wrlock(BlockDriverState *bs)
 {
+    AioContext *ctx = NULL;
+
     GLOBAL_STATE_CODE();
+    assert(!qatomic_read(&has_writer));
+    assert(!qemu_in_coroutine());
+
     /*
-     * TODO Some callers hold an AioContext lock when this is called, which
-     * causes deadlocks. Reenable once the AioContext locking is cleaned up (or
-     * AioContext locks are gone).
+     * Release only non-mainloop AioContext. The mainloop often relies on the
+     * BQL and doesn't lock the main AioContext before doing things.
      */
-#if 0
-    assert(!qatomic_read(&has_writer));
+    if (bs) {
+        ctx = bdrv_get_aio_context(bs);
+        if (ctx != qemu_get_aio_context()) {
+            aio_context_release(ctx);
+        } else {
+            ctx = NULL;
+        }
+    }
 
     /* Make sure that constantly arriving new I/O doesn't cause starvation */
     bdrv_drain_all_begin_nopoll();
@@ -149,31 +155,42 @@ void bdrv_graph_wrlock(void)
     } while (reader_count() >= 1);
 
     bdrv_drain_all_end();
-#endif
+
+    if (ctx) {
+        aio_context_acquire(bdrv_get_aio_context(bs));
+    }
 }
 
 void bdrv_graph_wrunlock(void)
 {
     GLOBAL_STATE_CODE();
-#if 0
-    QEMU_LOCK_GUARD(&aio_context_list_lock);
     assert(qatomic_read(&has_writer));
 
+    WITH_QEMU_LOCK_GUARD(&aio_context_list_lock) {
+        /*
+         * No need for memory barriers, this works in pair with
+         * the slow path of rdlock() and both take the lock.
+         */
+        qatomic_store_release(&has_writer, 0);
+
+        /* Wake up all coroutines that are waiting to read the graph */
+        qemu_co_enter_all(&reader_queue, &aio_context_list_lock);
+    }
+
     /*
-     * No need for memory barriers, this works in pair with
-     * the slow path of rdlock() and both take the lock.
+     * Run any BHs that were scheduled during the wrlock section and that
+     * callers might expect to have finished (in particular, this is important
+     * for bdrv_schedule_unref()).
+     *
+     * Do this only after restarting coroutines so that nested event loops in
+     * BHs don't deadlock if their condition relies on the coroutine making
+     * progress.
      */
-    qatomic_store_release(&has_writer, 0);
-
-    /* Wake up all coroutine that are waiting to read the graph */
-    qemu_co_enter_all(&reader_queue, &aio_context_list_lock);
-#endif
+    aio_bh_poll(qemu_get_aio_context());
 }
 
 void coroutine_fn bdrv_graph_co_rdlock(void)
 {
-    /* TODO Reenable when wrlock is reenabled */
-#if 0
     BdrvGraphRWlock *bdrv_graph;
     bdrv_graph = qemu_get_current_aio_context()->bdrv_graph;
 
@@ -233,12 +250,10 @@ void coroutine_fn bdrv_graph_co_rdlock(void)
             qemu_co_queue_wait(&reader_queue, &aio_context_list_lock);
         }
     }
-#endif
 }
 
 void coroutine_fn bdrv_graph_co_rdunlock(void)
 {
-#if 0
     BdrvGraphRWlock *bdrv_graph;
     bdrv_graph = qemu_get_current_aio_context()->bdrv_graph;
 
@@ -256,7 +271,6 @@ void coroutine_fn bdrv_graph_co_rdunlock(void)
     if (qatomic_read(&has_writer)) {
         aio_wait_kick();
     }
-#endif
 }
 
 void bdrv_graph_rdlock_main_loop(void)
@@ -274,19 +288,13 @@ void bdrv_graph_rdunlock_main_loop(void)
 void assert_bdrv_graph_readable(void)
 {
     /* reader_count() is slow due to aio_context_list_lock lock contention */
-    /* TODO Reenable when wrlock is reenabled */
-#if 0
 #ifdef CONFIG_DEBUG_GRAPH_LOCK
     assert(qemu_in_main_thread() || reader_count());
 #endif
-#endif
 }
 
 void assert_bdrv_graph_writable(void)
 {
     assert(qemu_in_main_thread());
-    /* TODO Reenable when wrlock is reenabled */
-#if 0
     assert(qatomic_read(&has_writer));
-#endif
 }