Hi!
On Fri 06-11-26 10:31:58, Bence Csókás wrote:
> On 2026. 11. 06. 10:05, Christian Brauner wrote:
> > On Tue, Oct 27, 2026 at 05:22:00PM +0100, Bence Csokas wrote:
> > > Add __free() support to eventfd and update drm_syncobj to use it as an
> > > example consumer.
> > >
> > > A minor discrepancy I encountered is whether to put a semicolon after
> > > DEFINE_FREE(). It seems some in-tree code does, some doesn't. In the end,
> > > I followed the example set in core-api/cleanup.rst, and omitted it.
> > >
> > > Signed-off-by: Bence Csokas <[email protected]>
> > > ---
> >
> > I'm really having trouble seeing how this improves anything
> > significantly. Probably others have the same impression which is why
> > this doesn't get a lot of review.
>
> The goal of the __free() API is to reduce the number of goto-based error
> paths. Normally, you'd have to keep the state of every local in your head
> for every early return. (Has it been initialized? Has it been consumed? Or
> does it need to be freed?) Then you need to arrange your "goto tree" (error
> labels) in a way that frees everything, and then for every early exit, jump
> to the correct one. This can be quite complex for some functions. Look at
> KVM or HyperV eventfd code, for example.
>
> By contrast, you just mark the local var with _free() and an appropriate
> destructor snippet, and the consumption point (the point after which we
> don't need to free it on a return) with no_free_ptr(), and the compiler
> instruments every early return accordingly.
Sure, but there's also the other side about which you don't speak: unless
the destructor is trivial (like kfree()), there are implications about
locking, when resources (such as references held by the object) get
released etc. So it can also be more complex to wrap your head around
__free usage than around standard cleanup code.
So unless __free is providing a noticeable simplification of some goto
hell, cleanup in many functions or similar, I generally don't find it worth
it...
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
