From: Mark Rutland <mark.rutland@arm.com>
To: Dawei Li <dawei.li@shingroup.cn>
Cc: catalin.marinas@arm.com, will@kernel.org, mcgrof@kernel.org,
jpoimboe@kernel.org, j.granados@samsung.com,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, set_pte_at@outlook.com
Subject: Re: [PATCH] arm64: remove unneeded BUILD_BUG_ON assertion
Date: Mon, 5 Feb 2024 12:06:18 +0000 [thread overview]
Message-ID: <ZcDPOgoQE8IncTHY@FVFF77S0Q05N> (raw)
In-Reply-To: <20240202040211.3118918-1-dawei.li@shingroup.cn>
On Fri, Feb 02, 2024 at 12:02:11PM +0800, Dawei Li wrote:
> Since commit c02433dd6de3 ("arm64: split thread_info from task stack"),
> CONFIG_THREAD_INFO_IN_TASK is enabled unconditionally for arm64. So
> remove this always-true assertion from arch_dup_task_struct.
>
> Signed-off-by: Dawei Li <dawei.li@shingroup.cn>
> ---
> arch/arm64/kernel/process.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 7387b68c745b..4ae31b7af6c3 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -290,9 +290,6 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
> fpsimd_preserve_current_state();
> *dst = *src;
>
> - /* We rely on the above assignment to initialize dst's thread_flags: */
> - BUILD_BUG_ON(!IS_ENABLED(CONFIG_THREAD_INFO_IN_TASK));
> -
Does the above cause any problem today, or is this patch just a cleanup?
For the benefit of other reviewers, the assertion and comment were added in
commit:
4585fc59c0e8 ("arm64/sve: Fix wrong free for task->thread.sve_state")
... back in 2019, 3 years after commit:
c02433dd6de3 ("arm64: split thread_info from task stack")
The comment and assertion were a safety-net for backports, since commit
4585fc59c0e8 was a fix which dependend upon the thread_info being contained
within task_struct, and couldn't be backported to kernels without
CONFIG_THREAD_INFO_IN_TASK.
I'm sure that we currently have plenty of other code with a similar (but
undocumented) dependency. Given we've unconditionally selected
CONFIG_THREAD_INFO_IN_TASK since v4.10, and the oldest longterm stable kernel
is v4.19 (with v4.14 having EOL'd last month), I think it makes sense to delete
the assertion and comment.
So FWIW:
Acked-by: Mark Rutland <mark.rutland@arm.com>
Mark.
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next prev parent reply other threads:[~2024-02-05 12:06 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-02 4:02 [PATCH] arm64: remove unneeded BUILD_BUG_ON assertion Dawei Li
2024-02-05 12:06 ` Mark Rutland [this message]
2024-02-06 1:39 ` Dawei Li
2024-02-22 9:27 ` Dawei Li
2024-02-22 22:05 ` Catalin Marinas
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