On 02.05.20 17:43, Markus Elfring wrote: > Hello, > > I have tried another small script out for the semantic patch language. > This source code analysis approach points out that the function “gmap_find_shadow” > is called two times by the function “gmap_shadow”. > https://elixir.bootlin.com/linux/v5.7-rc3/source/arch/s390/mm/gmap.c#L1628 > https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/log/arch/s390/mm/gmap.c > > Null pointer checks are performed at these places. Right, in case we have already a shadow, we return it. In case we are just concurrently creating/initializing another one, we return -EINVAL so the caller will retry (and find the fully initialized one). In case we get NULL, we have to create a new one. > The function “gmap_find_shadow” is documented in the same source file > that the pointer “ERR_PTR(-EAGAIN)” can eventually be returned. > Are the referenced gmap data structures always initialised here? -EAGAIN makes sure that we are not touching partially initialized one. In case we find a valid gmap shadow, it is fully initialized. That's what we have the ->initialized field for. Hope that answers your question. -- Thanks, David / dhildenb
