From 03ff63aa61b5504524ca64a2ed27c10da05a5126 Mon Sep 17 00:00:00 2001 From: Fiona Ebner Date: Tue, 17 Oct 2023 14:10:10 +0200 Subject: [PATCH] add patch to disable graph locking There are still some issues with graph locking, e.g. deadlocks during backup canceling [0] and initial attempts to fix it didn't work [1]. Because the AioContext locks still exist, it should still be safe to disable graph locking. [0]: https://lists.nongnu.org/archive/html/qemu-devel/2023-09/msg00729.html [1]: https://lists.nongnu.org/archive/html/qemu-devel/2023-09/msg06905.html Signed-off-by: Fiona Ebner Signed-off-by: Thomas Lamprecht --- ...t-graph-lock-Disable-locking-for-now.patch | 140 ++++++++++++++++++ debian/patches/series | 1 + 2 files changed, 141 insertions(+) create mode 100644 debian/patches/extra/0006-Revert-Revert-graph-lock-Disable-locking-for-now.patch diff --git a/debian/patches/extra/0006-Revert-Revert-graph-lock-Disable-locking-for-now.patch b/debian/patches/extra/0006-Revert-Revert-graph-lock-Disable-locking-for-now.patch new file mode 100644 index 0000000..f0648d2 --- /dev/null +++ b/debian/patches/extra/0006-Revert-Revert-graph-lock-Disable-locking-for-now.patch @@ -0,0 +1,140 @@ +From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 +From: Fiona Ebner +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 +--- + 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 + } diff --git a/debian/patches/series b/debian/patches/series index 01d4d3c..6d681da 100644 --- a/debian/patches/series +++ b/debian/patches/series @@ -3,6 +3,7 @@ extra/0002-scsi-megasas-Internal-cdbs-have-16-byte-length.patch extra/0003-ide-avoid-potential-deadlock-when-draining-during-tr.patch extra/0004-migration-block-dirty-bitmap-fix-loading-bitmap-when.patch extra/0005-hw-ide-reset-cancel-async-DMA-operation-before-reset.patch +extra/0006-Revert-Revert-graph-lock-Disable-locking-for-now.patch bitmap-mirror/0001-drive-mirror-add-support-for-sync-bitmap-mode-never.patch bitmap-mirror/0002-drive-mirror-add-support-for-conditional-and-always-.patch bitmap-mirror/0003-mirror-add-check-for-bitmap-mode-without-bitmap.patch