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[PATCH 2/2] block: Add no_coroutine_fn and coroutine_mixed_fn marker
From: |
Paolo Bonzini |
Subject: |
[PATCH 2/2] block: Add no_coroutine_fn and coroutine_mixed_fn marker |
Date: |
Thu, 15 Dec 2022 18:44:07 +0100 |
From: Alberto Faria <afaria@redhat.com>
Add more annotations to functions, describing valid and invalid
calls from coroutine to non-coroutine context.
When applied to a function, no_coroutine_fn advertises that it should
not be called from coroutine_fn functions. This can be because the
function blocks or, in the case of generated_co_wrapper, to enforce
that coroutine_fn functions directly call the coroutine_fn that backs
the generated_co_wrapper.
coroutine_mixed_fn instead is for function that can be called in
both coroutine and non-coroutine context, but will suspend when
called in coroutine context. Annotating them is a first step
towards enforcing that non-annotated functions are absolutely
not going to suspend.
These can be used for example with the vrc tool from
https://github.com/bonzini/vrc:
# find functions that *really* cannot be called from no_coroutine_fn
(vrc) load --loader clang
libblock.fa.p/meson-generated_.._block_block-gen.c.o
# The comma is an "AND". The "path" here consists of a single node
(vrc) paths [no_coroutine_fn,!coroutine_mixed_fn]
bdrv_remove_persistent_dirty_bitmap
bdrv_create
bdrv_can_store_new_dirty_bitmap
# find how coroutine_fns end up calling a mixed function
(vrc) load --loader clang --force libblock.fa.p/*.c.o
# regular expression search
(vrc) paths [coroutine_fn] [!no_coroutine_fn]* [coroutine_mixed_fn]
...
bdrv_pread <- vhdx_log_write <- vhdx_log_write_and_flush <- vhdx_co_writev
...
Signed-off-by: Alberto Faria <afaria@redhat.com>
[Rebase, add coroutine_mixed_fn. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
include/block/block-common.h | 11 +++++++----
include/qemu/coroutine.h | 33 +++++++++++++++++++++++++++++++++
2 files changed, 40 insertions(+), 4 deletions(-)
diff --git a/include/block/block-common.h b/include/block/block-common.h
index 4749c46a5e7e..cce79bd00135 100644
--- a/include/block/block-common.h
+++ b/include/block/block-common.h
@@ -50,11 +50,14 @@
* - co_wrapper_mixed_bdrv_rdlock are co_wrapper_mixed functions but
* automatically take and release the graph rdlock when creating a new
* coroutine.
+ *
+ * These functions should not be called from a coroutine_fn; instead,
+ * call the wrapped function directly.
*/
-#define co_wrapper
-#define co_wrapper_mixed
-#define co_wrapper_bdrv_rdlock
-#define co_wrapper_mixed_bdrv_rdlock
+#define co_wrapper no_coroutine_fn
+#define co_wrapper_mixed no_coroutine_fn coroutine_mixed_fn
+#define co_wrapper_bdrv_rdlock no_coroutine_fn
+#define co_wrapper_mixed_bdrv_rdlock no_coroutine_fn coroutine_mixed_fn
#include "block/dirty-bitmap.h"
#include "block/blockjob.h"
diff --git a/include/qemu/coroutine.h b/include/qemu/coroutine.h
index b0c97f6fb7ad..5f5ab8136a3a 100644
--- a/include/qemu/coroutine.h
+++ b/include/qemu/coroutine.h
@@ -28,6 +28,27 @@
* These functions are re-entrant and may be used outside the global mutex.
*/
+/**
+ * Mark a function that can suspend when executed in coroutine context,
+ * but can handle running in non-coroutine context too.
+ *
+ * Functions that execute in coroutine context cannot be called directly from
+ * normal functions. In the future it would be nice to enable compiler or
+ * static checker support for catching such errors. This annotation might make
+ * it possible and in the meantime it serves as documentation.
+ *
+ * For example:
+ *
+ * static void coroutine_fn foo(void) {
+ * ....
+ * }
+ */
+#ifdef __clang__
+#define coroutine_mixed_fn __attribute__((__annotate__("coroutine_mixed_fn")))
+#else
+#define coroutine_mixed_fn
+#endif
+
/**
* Mark a function that executes in coroutine context
*
@@ -48,6 +69,18 @@
#define coroutine_fn
#endif
+/**
+ * Mark a function that should never be called from a coroutine context
+ *
+ * This typically means that there is an analogous, coroutine_fn function that
+ * should be used instead.
+ */
+#ifdef __clang__
+#define no_coroutine_fn __attribute__((__annotate__("no_coroutine_fn")))
+#else
+#define no_coroutine_fn
+#endif
+
typedef struct Coroutine Coroutine;
/**
--
2.38.1