# Re: \[PATCH v3\] proc,fcntl: introduce F\_SET\_DESCRIPTION

- From: Pascal Bouchareine \<hidden\>
- Date: 2020-07-28 01:39:53 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2020/07/185375
- Thread: https://ratatoskr.run/linux-fsdevel/2020/07/185191/t.md

```text
Thanks for reviewing, I added some questions inline below

On Mon, Jul 27, 2020 at 7:21 AM Alexey Dobriyan [ref] wrote:
> > +     d = strndup_user(desc, MAX_FILE_DESC_SIZE);
>
> This should be kmem accounted because allocation is persistent.
> To make things more entertaining, strndup_user() doesn't have gfp_t argument.

I had to look it up so I might be very far from it, but is that
__GFP_ACCOUNT and would it be correct to assume memdup_user() should
use it unconditionally?

Otherwise my simple option would be to implement the logic in the
set_description, but the benefit would be very local.

Please let me know what you think is best, happy to read more doc if
there's a more productive way to address that

>
> > +     if (IS_ERR(d))
> > +             return PTR_ERR(d);
> > +
> > +     spin_lock(&file->f_lock);
> > +     kfree(file->f_description);
> > +     file->f_description = d;
> > +     spin_unlock(&file->f_lock);
>
> Generally kfree under spinlock is not good idea.
> You can replace the pointer and free without spinlock.

Sorry I also need some pointers here - do you suggest I move the kfree
out of the locked section or that there is a safe way other than
spinlock?

> struct file is nicely aligned to 256 bytes on distro configs.
> Will this break everything?
>
>         $ cat /sys/kernel/slab/filp/object_size

Indeed on the config I'm using here this jumped to 264 bytes

Would it be better to move this to the inode struct? I don't know the
implications of this - any other option?

Thanks!
```