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Revert "graph-lock: Disable locking for now" 

Now that bdrv_graph_wrlock() temporarily drops the AioContext lock that
its caller holds, it can poll without causing deadlocks. We can now
re-enable graph locking.

This reverts commit ad128dff0bf4b6f971d05eb4335a627883a19c1d.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230605085711.21261-12-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2023-06-05 10:57:11 +02:00
parent 31b2ddfea3
commit 3cce22defb
1 changed files with 0 additions and 26 deletions
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26
block/graph-lock.c
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@ -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;
@ -108,21 +105,13 @@ static uint32_t reader_count(void)
assert((int32_t)rd >= 0);
return rd;
}
#endif
void bdrv_graph_wrlock(BlockDriverState *bs)
{
AioContext *ctx = NULL;
GLOBAL_STATE_CODE();
/*
* 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).
*/
#if 0
assert(!qatomic_read(&has_writer));
#endif
/*
* Release only non-mainloop AioContext. The mainloop often relies on the
@ -137,7 +126,6 @@ void bdrv_graph_wrlock(BlockDriverState *bs)
}
}
#if 0
/* Make sure that constantly arriving new I/O doesn't cause starvation */
bdrv_drain_all_begin_nopoll();
@ -166,7 +154,6 @@ void bdrv_graph_wrlock(BlockDriverState *bs)
} while (reader_count() >= 1);
bdrv_drain_all_end();
#endif
if (ctx) {
aio_context_acquire(bdrv_get_aio_context(bs));
@ -176,7 +163,6 @@ void bdrv_graph_wrlock(BlockDriverState *bs)
void bdrv_graph_wrunlock(void)
{
GLOBAL_STATE_CODE();
#if 0
QEMU_LOCK_GUARD(&aio_context_list_lock);
assert(qatomic_read(&has_writer));
@ -188,13 +174,10 @@ void bdrv_graph_wrunlock(void)
/* Wake up all coroutine that are waiting to read the graph */
qemu_co_enter_all(&reader_queue, &aio_context_list_lock);
#endif
}
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;
@ -254,12 +237,10 @@ 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;
@ -277,7 +258,6 @@ void coroutine_fn bdrv_graph_co_rdunlock(void)
if (qatomic_read(&has_writer)) {
aio_wait_kick();
}
#endif
}
void bdrv_graph_rdlock_main_loop(void)
@ -295,19 +275,13 @@ 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
}