141 lines
4.0 KiB
Diff
141 lines
4.0 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
|
|
From: Fiona Ebner <f.ebner@proxmox.com>
|
|
Date: Thu, 28 Sep 2023 10:07:03 +0200
|
|
Subject: [PATCH] Revert "Revert "graph-lock: Disable locking for now""
|
|
|
|
This reverts commit 3cce22defb4b0e47cf135444e30cc673cff5ebad.
|
|
|
|
There are still some issues with graph locking, e.g. deadlocks during
|
|
backup canceling [0]. Because the AioContext locks still exist, it
|
|
should be safe to disable locking again.
|
|
|
|
From the original 80fc5d2600 ("graph-lock: Disable locking for now"):
|
|
|
|
> We don't currently rely on graph locking yet. It is supposed to replace
|
|
> the AioContext lock eventually to enable multiqueue support, but as long
|
|
> as we still have the AioContext lock, it is sufficient without the graph
|
|
> lock. Once the AioContext lock goes away, the deadlock doesn't exist any
|
|
> more either and this commit can be reverted. (Of course, it can also be
|
|
> reverted while the AioContext lock still exists if the callers have been
|
|
> fixed.)
|
|
|
|
[0]: https://lists.nongnu.org/archive/html/qemu-devel/2023-09/msg00729.html
|
|
|
|
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
|
|
---
|
|
block/graph-lock.c | 24 ++++++++++++++++++++++++
|
|
1 file changed, 24 insertions(+)
|
|
|
|
diff --git a/block/graph-lock.c b/block/graph-lock.c
|
|
index 5e66f01ae8..5c2873262a 100644
|
|
--- a/block/graph-lock.c
|
|
+++ b/block/graph-lock.c
|
|
@@ -30,8 +30,10 @@ 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.
|
|
@@ -88,6 +90,7 @@ void unregister_aiocontext(AioContext *ctx)
|
|
g_free(ctx->bdrv_graph);
|
|
}
|
|
|
|
+#if 0
|
|
static uint32_t reader_count(void)
|
|
{
|
|
BdrvGraphRWlock *brdv_graph;
|
|
@@ -105,12 +108,19 @@ static uint32_t reader_count(void)
|
|
assert((int32_t)rd >= 0);
|
|
return rd;
|
|
}
|
|
+#endif
|
|
|
|
void bdrv_graph_wrlock(BlockDriverState *bs)
|
|
{
|
|
+#if 0
|
|
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).
|
|
+ */
|
|
assert(!qatomic_read(&has_writer));
|
|
|
|
/*
|
|
@@ -158,11 +168,13 @@ void bdrv_graph_wrlock(BlockDriverState *bs)
|
|
if (ctx) {
|
|
aio_context_acquire(bdrv_get_aio_context(bs));
|
|
}
|
|
+#endif
|
|
}
|
|
|
|
void bdrv_graph_wrunlock(void)
|
|
{
|
|
GLOBAL_STATE_CODE();
|
|
+#if 0
|
|
QEMU_LOCK_GUARD(&aio_context_list_lock);
|
|
assert(qatomic_read(&has_writer));
|
|
|
|
@@ -174,10 +186,13 @@ 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;
|
|
|
|
@@ -237,10 +252,12 @@ 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;
|
|
|
|
@@ -258,6 +275,7 @@ void coroutine_fn bdrv_graph_co_rdunlock(void)
|
|
if (qatomic_read(&has_writer)) {
|
|
aio_wait_kick();
|
|
}
|
|
+#endif
|
|
}
|
|
|
|
void bdrv_graph_rdlock_main_loop(void)
|
|
@@ -275,13 +293,19 @@ 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
|
|
}
|