Re: [PATCH v3 1/3] exec: separate thread_count for files_struct

[Oleg Nesterov]

On 09/16, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@xxxxxxxxxx> writes:
>
> > As for binder.c, in this case we probably actually want to unshare ->files
> > on exec so we can ignore it?
>
> Looking at the binder case it only captures ->files on mmap.  Exec
> ditches the mmap.  So if the order of operations are correct than
> the dropping of the old mm will also drop the count on files_struct
> held by binder.
>
> So semantically binder should not effect locks on exec,

Agreed, but it does.

Before your "[PATCH 0/3] exec: Moving unshare_files_struct" unshare_files()
is called before exec_mmap().

And even with this series we can have another CLONE_VM process.

Howver, I think this doesn't really matter. binder does __fd_install(files),
so if it actually has a reference to execing_task->files, I think it should
be unshared anyway.

> In short as long as we get the oder of operations correct we should be
> able to safely ignore binder, and not have binder affect the results of
> this code.

Agreed.

Oleg.