Re: [PATCH v3 10/13] preempt: Introduce HAS_SEPARATE_PREEMPT_RESCHED_BITS

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Unconditional select of `HAS_SEPARATE_PREEMPT_RESCHED_BITS` violates Kconfig dependency on `PREEMPT_COUNT`.
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commit 0d37eeeba0d2e4fb4b795207e44eb2cab20db648
Author: Boqun Feng <boqun@kernel.org>

preempt: Introduce HAS_SEPARATE_PREEMPT_RESCHED_BITS

This commit introduces HAS_SEPARATE_PREEMPT_RESCHED_BITS to allow 64-bit 
architectures to maintain NMI nesting bits in the 32-bit preempt count, 
avoiding the need to maintain them outside the same cache line. It also 
enables this feature for x86_64.

Originally-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Boqun Feng <boqun@kernel.org>

> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index fdaef60b46d65..9a35c3a087573 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -329,6 +329,7 @@ config X86
>  	select USER_STACKTRACE_SUPPORT
>  	select HAVE_ARCH_KCSAN			if X86_64
>  	select PROC_PID_ARCH_STATUS		if PROC_FS
> +	select HAS_SEPARATE_PREEMPT_RESCHED_BITS		if X86_64

[Severity: Medium]
Will selecting HAS_SEPARATE_PREEMPT_RESCHED_BITS unconditionally for X86_64 
cause Kconfig unmet direct dependency warnings if PREEMPT_COUNT is disabled?

Looking at the definition in kernel/Kconfig.preempt, the config symbol 
HAS_SEPARATE_PREEMPT_RESCHED_BITS explicitly depends on PREEMPT_COUNT:

config HAS_SEPARATE_PREEMPT_RESCHED_BITS
    bool
    depends on PREEMPT_COUNT && 64BIT

Because select bypasses depends on, configuring a kernel where PREEMPT_COUNT
is disabled (e.g., PREEMPT_NONE=y with no debug options) might force the 
target symbol to y. Should this select be conditional on PREEMPT_COUNT?

>  	select HAVE_ARCH_NODE_DEV_GROUP		if X86_SGX
>  	select FUNCTION_ALIGNMENT_16B		if X86_64 || X86_ALIGNMENT_16
>  	select FUNCTION_ALIGNMENT_4B

[ ... ]

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Sashiko AI review · https://sashiko.dev/#/patchset/20260605054128.5925-1-boqun@kernel.org?part=10