22 #include "qemu/main-loop.h"
23 #include "block/graph-lock.h"
33 /* Written and read with atomic operations. */
37  * Many write-locked sections are also drained sections. There is a convenience
41  * because the aio_poll() call in bdrv_graph_wrlock() might re-enter
43  * bdrv_graph_wrunlock() might also re-enter a write-locked section.
66      * List of BdrvGraphRWlock kept in graph-lock.c
88     ctx->bdrv_graph = g_new0(BdrvGraphRWlock, 1);  in register_aiocontext()
90     assert(ctx->bdrv_graph->reader_count == 0);  in register_aiocontext()
91     QTAILQ_INSERT_TAIL(&aio_context_list, ctx->bdrv_graph, next_aio);  in register_aiocontext()
97     orphaned_reader_count += ctx->bdrv_graph->reader_count;  in unregister_aiocontext()
98     QTAILQ_REMOVE(&aio_context_list, ctx->bdrv_graph, next_aio);  in unregister_aiocontext()
99     g_free(ctx->bdrv_graph);  in unregister_aiocontext()
112         rd += qatomic_read(&brdv_graph->reader_count);  in reader_count()
136      * reader_count == 0: this means writer will read has_reader as 1  in bdrv_graph_wrlock()
137      * reader_count >= 1: we don't know if writer read has_writer == 0 or 1,  in bdrv_graph_wrlock()
138      *                    but we need to wait.  in bdrv_graph_wrlock()
139      * Wait by allowing other coroutine (and possible readers) to continue.  in bdrv_graph_wrlock()
185         /* Wake up all coroutines that are waiting to read the graph */  in bdrv_graph_wrunlock()
195      * BHs don't deadlock if their condition relies on the coroutine making  in bdrv_graph_wrunlock()
202         wrlock_quiesced_counter--;  in bdrv_graph_wrunlock()
210     bdrv_graph = qemu_get_current_aio_context()->bdrv_graph;  in bdrv_graph_co_rdlock()
213         qatomic_set(&bdrv_graph->reader_count,  in bdrv_graph_co_rdlock()
214                     bdrv_graph->reader_count + 1);  in bdrv_graph_co_rdlock()
219          * has_writer == 0: this means writer will read reader_count as >= 1  in bdrv_graph_co_rdlock()
220          * has_writer == 1: we don't know if writer read reader_count == 0  in bdrv_graph_co_rdlock()
221          *                  or > 0, but we need to wait anyways because  in bdrv_graph_co_rdlock()
233          * Then the writer will read reader_count that does not take into  in bdrv_graph_co_rdlock()
238          * then writer will read reader_count >= 1.  in bdrv_graph_co_rdlock()
239          * It will wait in AIO_WAIT_WHILE(), but once it releases the lock  in bdrv_graph_co_rdlock()
263             bdrv_graph->reader_count--;  in bdrv_graph_co_rdlock()
273     bdrv_graph = qemu_get_current_aio_context()->bdrv_graph;  in bdrv_graph_co_rdunlock()
275     qatomic_store_release(&bdrv_graph->reader_count,  in bdrv_graph_co_rdunlock()
276                           bdrv_graph->reader_count - 1);  in bdrv_graph_co_rdunlock()
281      * has_writer == 0: this means reader will read reader_count decreased  in bdrv_graph_co_rdunlock()
282      * has_writer == 1: we don't know if writer read reader_count old or  in bdrv_graph_co_rdunlock()
283      *                  new. Therefore, kick again so on next iteration  in bdrv_graph_co_rdunlock()
284      *                  writer will for sure read the updated value.  in bdrv_graph_co_rdunlock()