Re: [Tarantool-patches] [PATCH 1/1] swim: don't call swim_quit via FFI

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

Hi! Thanks for the review!

On 23.11.2020 14:40, Igor Munkin wrote:
> Vlad,
> 
> Thanks for the patch! LGTM, with a couple nits below.
> 
> On 20.11.20, Vladislav Shpilevoy wrote:
>> swim_quit yields, because it joins the event handler fiber. Hence
>> it can't be called via FFI, where a yield leads to undefined
>> behaviour.
> 
> Minor: I wouldn't call this UB, let's reword it "where a yield might
> lead to the platform panic".

Agree, applied.

>> diff --git a/src/lua/swim.c b/src/lua/swim.c
>> index ae916bf78..b9c9dd635 100644
>> --- a/src/lua/swim.c
>> +++ b/src/lua/swim.c
>> @@ -88,6 +88,19 @@ lua_swim_delete(struct lua_State *L)
>>  	return 0;
>>  }
>>  
>> +/**
>> + * Gracefully leave the cluster, broadcast a notification, and delete the SWIM
>> + * instance. It is not FFI, because this operation yields.
>> + */
>> +static int
>> +lua_swim_quit(struct lua_State *L)
>> +{
>> +	uint32_t ctypeid;
>> +	struct swim *s = *(struct swim **) luaL_checkcdata(L, 1, &ctypeid);
> 
> Minor: I don't know whether it's common practice in Tarantool, but
> assert that <ctypeid> equals to <ctid_swim_ptr> would be nice here.
> Feel free to ignore.

I added it to quit and delete.

The new patch is below:

====================
    swim: don't call swim_quit via FFI
    
    swim_quit yields, because it joins the event handler fiber. Hence
    it can't be called via FFI, where a yield might lead to platform
    panic.
    
    Closes #4570

diff --git a/src/lua/swim.c b/src/lua/swim.c
index ae916bf78..cfce50e1a 100644
--- a/src/lua/swim.c
+++ b/src/lua/swim.c
@@ -84,10 +84,25 @@ lua_swim_delete(struct lua_State *L)
 {
 	uint32_t ctypeid;
 	struct swim *s = *(struct swim **) luaL_checkcdata(L, 1, &ctypeid);
+	assert(ctypeid == ctid_swim_ptr);
 	swim_delete(s);
 	return 0;
 }
 
+/**
+ * Gracefully leave the cluster, broadcast a notification, and delete the SWIM
+ * instance. It is not FFI, because this operation yields.
+ */
+static int
+lua_swim_quit(struct lua_State *L)
+{
+	uint32_t ctypeid;
+	struct swim *s = *(struct swim **) luaL_checkcdata(L, 1, &ctypeid);
+	assert(ctypeid == ctid_swim_ptr);
+	swim_quit(s);
+	return 0;
+}
+
 void
 tarantool_lua_swim_init(struct lua_State *L)
 {
@@ -98,6 +113,7 @@ tarantool_lua_swim_init(struct lua_State *L)
 	static const struct luaL_Reg lua_swim_internal_methods [] = {
 		{"swim_new", lua_swim_new},
 		{"swim_delete", lua_swim_delete},
+		{"swim_quit", lua_swim_quit},
 		{"swim_on_member_event", lua_swim_on_member_event},
 		{NULL, NULL}
 	};
diff --git a/src/lua/swim.lua b/src/lua/swim.lua
index c1ab1c5c3..1da55337a 100644
--- a/src/lua/swim.lua
+++ b/src/lua/swim.lua
@@ -74,9 +74,6 @@ ffi.cdef[[
     int
     swim_size(const struct swim *swim);
 
-    void
-    swim_quit(struct swim *swim);
-
     struct swim_member *
     swim_self(struct swim *swim);
 
@@ -519,7 +516,7 @@ end
 --
 local function swim_quit(s)
     local ptr = swim_check_instance(s, 'swim:quit')
-    capi.swim_quit(ffi.gc(ptr, nil))
+    internal.swim_quit(ffi.gc(ptr, nil))
     s.ptr = nil
     setmetatable(s, swim_mt_deleted)
 end