Re: [PATCH/RFC 1/2] anon-inodes: Remove fd_install() from anon_inode_getfd()

Davide Libenzi
2008-02-28T20:04:26Z

On Wed, 27 Feb 2008, Roland Dreier wrote:

> > http://git.kernel.org/?p=linux/kernel/git/viro/vfs-2.6.git;a=commit;h=49be4f8114e6ff0efdab10ebba2493fb67bc3034
>
> Actually, looking closer at the kvm changes here, I think that
> create_vcpu_fd() needs the same treatment as kvm_dev_ioctl_create_vm()
> gets in the patch because of the race I mentioned in the changelog
> for my patch: otherwise kvm_vcpu_release() could drop the last
> reference to vcpu->kvm->filp before the get_file() gets an extra
> reference.
>
> I'm beginning to think that moving the fd_install() out of
> anon_inode_getfd() really is worth it to make a safer interface.

If we let the caller call fd_install(), then it may be messed up WRT
cleanup (fd, file, inode).
How about removing the inode pointer handout altogether, and *doing*
fd_install() inside anon_inode_getfd() like:

if (pfile != NULL) {
get_file(file);
*pfile = file;
}
fd_install(fd, file);

In this way, if the caller want the file* back, he gets the reference
bumped before fd_install().

- Davide