linux-kernel - RE: [PATCH v3 12/13] rust: sync: reduce stack usage of `UniqueArc::try_new

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Message-ID: <7f55875c46ab4c4989323ede57f6e46d@AcuMS.aculab.com>
Date:   Thu, 30 Mar 2023 14:58:24 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'y86-dev@...tonmail.com'" <y86-dev@...tonmail.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Alice Ryhl <alice@...l.io>
CC:     "rust-for-linux@...r.kernel.org" <rust-for-linux@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>
Subject: RE: [PATCH v3 12/13] rust: sync: reduce stack usage of
 `UniqueArc::try_new_uninit`

From: y86-dev@...tonmail.com
> Sent: 29 March 2023 23:34
> 
> `UniqueArc::try_new_uninit` calls `Arc::try_new(MaybeUninit::uninit())`.
> This results in the uninitialized memory being placed on the stack,
> which may be arbitrarily large due to the generic `T` and thus could
> cause a stack overflow for large types.

Does that mean rust is using (the equivalent of) alloca() ?

That is banned for C code in the kernel for any sizes.

	David

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