From: "Arnd Bergmann" <arnd@arndb.de>
To: "Matt Evans" <mev@rivosinc.com>,
linux-kernel@vger.kernel.org,
Linux-Arch <linux-arch@vger.kernel.org>
Cc: "Palmer Dabbelt" <palmer@rivosinc.com>
Subject: Re: [PATCH] locking/atomic: cmpxchg: Make __generic_cmpxchg_local compare against zero-extended 'old' value
Date: Fri, 03 Feb 2023 15:32:28 +0100 [thread overview]
Message-ID: <a55d3d15-d89d-43c4-85e7-c6d18a57a32f@app.fastmail.com> (raw)
In-Reply-To: <8B94CEAB-63AD-400F-A5CD-31AC4490EF4C@rivosinc.com>
On Wed, Feb 1, 2023, at 19:39, Matt Evans wrote:
> __generic_cmpxchg_local takes unsigned long old/new arguments which
> might end up being up-cast from smaller signed types (which will
> sign-extend). The loaded compare value must be compared against a
> truncated smaller type, so down-cast appropriately for each size.
>
> The issue is apparent on 64-bit machines with code, such as
> atomic_dec_unless_positive(), that sign-extends from int.
>
> 64-bit machines generally don't use the generic cmpxchg but
> development/early ports might make use of it, so make it correct.
>
> Signed-off-by: Matt Evans <mev@rivosinc.com>
> ---
Applied to the asm-generic tree for 6.3, thanks
Arnd
next prev parent reply other threads:[~2023-02-03 14:33 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-01 18:39 Matt Evans
2023-02-03 14:32 ` Arnd Bergmann [this message]
2023-02-26 10:13 ` Arnd Bergmann
2023-03-01 15:19 ` Matt Evans
2023-03-01 16:22 ` Arnd Bergmann
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