block-coroutine-wrapper: Take AioContext lock in no_co_wrappers

All of the functions that currently take a BlockDriverState, BdrvChild
or BlockBackend as their first parameter expect the associated
AioContext to be locked when they are called. In the case of
no_co_wrappers, they are called from bottom halves directly in the main
loop, so no other caller can be expected to take the lock for them. This
can result in assertion failures because a lock that isn't taken is
released in nested event loops.

Looking at the first parameter is already done by co_wrappers to decide
where the coroutine should run, so doing the same in no_co_wrappers is
only consistent. Take the lock in the generated bottom halves to fix the
problem.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230525124713.401149-2-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 15 insertions, 10 deletions

diff --git a/scripts/block-coroutine-wrapper.py b/scripts/block-coroutine-wrapper.py
index 60e9b3107c..d4a183db61 100644
--- a/scripts/block-coroutine-wrapper.py
+++ b/scripts/block-coroutine-wrapper.py
@@ -88,16 +88,7 @@ class FuncDecl:
                 raise ValueError(f"no_co function can't be rdlock: {self.name}")
             self.target_name = f'{subsystem}_{subname}'
 
-        t = self.args[0].type
-        if t == 'BlockDriverState *':
-            ctx = 'bdrv_get_aio_context(bs)'
-        elif t == 'BdrvChild *':
-            ctx = 'bdrv_get_aio_context(child->bs)'
-        elif t == 'BlockBackend *':
-            ctx = 'blk_get_aio_context(blk)'
-        else:
-            ctx = 'qemu_get_aio_context()'
-        self.ctx = ctx
+        self.ctx = self.gen_ctx()
 
         self.get_result = 's->ret = '
         self.ret = 'return s.ret;'
@@ -109,6 +100,17 @@ class FuncDecl:
             self.co_ret = ''
             self.return_field = ''
 
+    def gen_ctx(self, prefix: str = '') -> str:
+        t = self.args[0].type
+        if t == 'BlockDriverState *':
+            return f'bdrv_get_aio_context({prefix}bs)'
+        elif t == 'BdrvChild *':
+            return f'bdrv_get_aio_context({prefix}child->bs)'
+        elif t == 'BlockBackend *':
+            return f'blk_get_aio_context({prefix}blk)'
+        else:
+            return 'qemu_get_aio_context()'
+
     def gen_list(self, format: str) -> str:
         return ', '.join(format.format_map(arg.__dict__) for arg in self.args)
 
@@ -262,8 +264,11 @@ typedef struct {struct_name} {{
 static void {name}_bh(void *opaque)
 {{
     {struct_name} *s = opaque;
+    AioContext *ctx = {func.gen_ctx('s->')};
 
+    aio_context_acquire(ctx);
     {func.get_result}{name}({ func.gen_list('s->{name}') });
+    aio_context_release(ctx);
 
     aio_co_wake(s->co);
 }}