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Message-ID: <aBIUUs4AWTII2bcO@google.com>
Date: Wed, 30 Apr 2025 12:15:14 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: Danilo Krummrich <dakr@...nel.org>, Matthew Maurer <mmaurer@...gle.com>, rust-for-linux@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 7/7] rust: alloc: add Vec::insert_within_capacity
On Wed, Apr 30, 2025 at 01:39:03PM +0200, Greg KH wrote:
> On Wed, Apr 30, 2025 at 11:24:23AM +0000, Alice Ryhl wrote:
> > On Tue, Apr 29, 2025 at 05:30:06PM +0200, Greg KH wrote:
> > > On Tue, Apr 29, 2025 at 02:44:27PM +0000, Alice Ryhl wrote:
> > > > This adds a variant of Vec::insert that does not allocate memory. This
> > > > makes it safe to use this function while holding a spinlock. Rust Binder
> > > > uses it for the range allocator fast path.
> > > >
> > > > Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> > > > ---
> > > > rust/kernel/alloc/kvec.rs | 39 +++++++++++++++++++++++++++++++++++++++
> > > > 1 file changed, 39 insertions(+)
> > > >
> > > > diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
> > > > index 0682108951675cbee05faa130e5a9ce72fc343ba..998afdcde47bec94b2c9d990ba3afbb3488ea99e 100644
> > > > --- a/rust/kernel/alloc/kvec.rs
> > > > +++ b/rust/kernel/alloc/kvec.rs
> > > > @@ -355,6 +355,45 @@ pub unsafe fn push_within_capacity_unchecked(&mut self, v: T) {
> > > > unsafe { self.inc_len(1) };
> > > > }
> > > >
> > > > + /// Inserts an element at the given index in the [`Vec`] instance.
> > > > + ///
> > > > + /// Fails if the vector does not have capacity for the new element. Panics if the index is out
> > > > + /// of bounds.
> > >
> > > Why panic and why not just return an error instead?
> >
> > It's for consistency with stdlib. Illegal use is panic, expected error
> > conditions are errors.
>
> But this is the kernel, not userspace :)
>
> As you can return an error, why not? Rebooting a box should be a "last
> resort" type of thing when you can not recover from an error. You can
> easily not overflow and return an error here, so why do you want to just
> give up and cause all data to be lost?
>
> And I don't see any other panics happening in this file, so would this
> be the first one?
I don't feel strongly about this method, but it's not the first panic.
The vector type has an indexing operator vec[i] that panics if you index
out-of-bounds.
Alice
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