[Libguestfs] [PATCH] lua: improve handle closing
Richard W.M. Jones
rjones at redhat.com
Wed Sep 10 16:19:48 UTC 2014
On Wed, Sep 10, 2014 at 01:13:07PM +0200, Pino Toscano wrote:
> Swap guestfs_close and free_per_handle_table, so first the handle is
> removed from the table and then freed. This avoids passing a stale
> pointer to free_per_handle_table (which right now is not an issue, but
> better make sure it is never so).
> ---
> Maybe this could also fix the case described by the comment there,
> as when a new 'g' with the address of an old 'g' would be created,
> the old 'g' is now already gone from the per-handle table.
>
> generator/lua.ml | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/generator/lua.ml b/generator/lua.ml
> index 5d5619c..fa6e9f2 100644
> --- a/generator/lua.ml
> +++ b/generator/lua.ml
> @@ -168,13 +168,13 @@ guestfs_lua_create (lua_State *L)
> static void
> close_handle (lua_State *L, guestfs_h *g)
> {
> - guestfs_close (g);
> /* There is a potential and hard-to-solve race here: If another
> * thread allocates another 'g' at the same address, then
> * get_per_handle_table might be called with the same address
> * before we call free_per_handle_table here. XXX
> */
> free_per_handle_table (L, g);
> + guestfs_close (g);
> }
I have a vague feeling that the order of operations here was important
for some reason. And presumably I wouldn't have written that comment
if the solution was as simple as swapping the two statements around.
So .. not sure. I think we should leave this alone.
I can't find anything in the git commits to indicate what the problem
might have been.
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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