linux-kernel - Re: [PATCH 1/5] export file_close_fd and task_work

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Message-ID: <aYrwuPus_cOyumGo@google.com>
Date: Tue, 10 Feb 2026 08:47:52 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Carlos Llamas <cmllamas@...gle.com>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
	Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>, 
	"Serge E. Hallyn" <serge@...lyn.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Dave Chinner <david@...morbit.com>, Qi Zheng <zhengqi.arch@...edance.com>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Muchun Song <muchun.song@...ux.dev>, 
	David Hildenbrand <david@...nel.org>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>, 
	Michal Hocko <mhocko@...e.com>, Miguel Ojeda <ojeda@...nel.org>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, kernel-team@...roid.com, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org, 
	linux-mm@...ck.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 1/5] export file_close_fd and task_work_add

On Mon, Feb 09, 2026 at 03:21:58PM +0000, Lorenzo Stoakes wrote:
> On Thu, Feb 05, 2026 at 01:45:40PM +0000, Alice Ryhl wrote:
> > +/**
> > + * close_fd_safe - close the given fd
> > + * @fd: file descriptor to close
> > + * @flags: gfp flags for allocation of task work
> > + *
> > + * This closes an fd. Unlike close_fd(), this may be used even if the fd is
> > + * currently held with fdget().
> > + *
> > + * Returns: 0 or an error code
> > + */
> > +int close_fd_safe(unsigned int fd, gfp_t flags)
> > +{
> > +	struct close_fd_safe_task_work *twcb;
> > +
> > +	twcb = kzalloc(sizeof(*twcb), flags);
> > +	if (!twcb)
> > +		return -ENOMEM;
> > +	init_task_work(&twcb->twork, close_fd_safe_callback);
> > +	twcb->file = file_close_fd(fd);
> > +	if (!twcb->file) {
> > +		kfree(twcb);
> > +		return -EBADF;
> > +	}
> > +
> > +	get_file(twcb->file);
> > +	filp_close(twcb->file, current->files);
> > +	task_work_add(current, &twcb->twork, TWA_RESUME);
> > +	return 0;
> > +}
> 
> Would need an EXPORT_SYMBOL_FOR_MODULES(...) here right?

Ah yeah, for Binder to become a module it would need to be exported.
(Though maybe it's worth moving this logic even if Binder is not made
into a module?)

> > diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
> > index c45306a9f007..1c99a56c0cdf 100644
> > --- a/include/linux/fdtable.h
> > +++ b/include/linux/fdtable.h
> > @@ -111,6 +111,7 @@ int iterate_fd(struct files_struct *, unsigned,
> >  		const void *);
> >
> >  extern int close_fd(unsigned int fd);
> > +extern int close_fd_safe(unsigned int fd, gfp_t flags);
> 
> One nit, generally well in mm anyway we avoid the 'extern' and remove them as we
> go. Not sure about vfs actually though?

Right. Not sure about this.

> >  extern struct file *file_close_fd(unsigned int fd);
> >
> >  extern struct kmem_cache *files_cachep;
> 
> I mean this is essentially taking what's in binder and making it a general
> thing, so needs Christian's input on whether this is sensible I think :)

Yeah.

Alice