diff options
Diffstat (limited to 'block/graph-lock.c')
| -rw-r--r-- | block/graph-lock.c | 40 |
1 files changed, 37 insertions, 3 deletions
diff --git a/block/graph-lock.c b/block/graph-lock.c index c81162b..b731947 100644 --- a/block/graph-lock.c +++ b/block/graph-lock.c @@ -34,6 +34,17 @@ static QemuMutex aio_context_list_lock; static int has_writer; /* + * Many write-locked sections are also drained sections. There is a convenience + * wrapper bdrv_graph_wrlock_drained() which begins a drained section before + * acquiring the lock. This variable here is used so bdrv_graph_wrunlock() knows + * if it also needs to end such a drained section. It needs to be a counter, + * because the aio_poll() call in bdrv_graph_wrlock() might re-enter + * bdrv_graph_wrlock_drained(). And note that aio_bh_poll() in + * bdrv_graph_wrunlock() might also re-enter a write-locked section. + */ +static int wrlock_quiesced_counter; + +/* * A reader coroutine could move from an AioContext to another. * If this happens, there is no problem from the point of view of * counters. The problem is that the total count becomes @@ -112,8 +123,14 @@ void no_coroutine_fn bdrv_graph_wrlock(void) assert(!qatomic_read(&has_writer)); assert(!qemu_in_coroutine()); - /* Make sure that constantly arriving new I/O doesn't cause starvation */ - bdrv_drain_all_begin_nopoll(); + bool need_drain = wrlock_quiesced_counter == 0; + + if (need_drain) { + /* + * Make sure that constantly arriving new I/O doesn't cause starvation + */ + bdrv_drain_all_begin_nopoll(); + } /* * reader_count == 0: this means writer will read has_reader as 1 @@ -139,7 +156,18 @@ void no_coroutine_fn bdrv_graph_wrlock(void) smp_mb(); } while (reader_count() >= 1); - bdrv_drain_all_end(); + if (need_drain) { + bdrv_drain_all_end(); + } +} + +void no_coroutine_fn bdrv_graph_wrlock_drained(void) +{ + GLOBAL_STATE_CODE(); + + bdrv_drain_all_begin(); + wrlock_quiesced_counter++; + bdrv_graph_wrlock(); } void no_coroutine_fn bdrv_graph_wrunlock(void) @@ -168,6 +196,12 @@ void no_coroutine_fn bdrv_graph_wrunlock(void) * progress. */ aio_bh_poll(qemu_get_aio_context()); + + if (wrlock_quiesced_counter > 0) { + bdrv_drain_all_end(); + wrlock_quiesced_counter--; + } + } void coroutine_fn bdrv_graph_co_rdlock(void) |