Re: [PATCH v15 02/16] arm64: barrier: Support smp_cond_load_relaxed_timeout()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] Module linkage failure due to unexported symbol `arch_timer_evtstrm_available`.
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commit 6f96330ea583f1ff6aede67a83cdc552196dad11
Author: Ankur Arora <ankur.a.arora@oracle.com>

arm64: barrier: Support smp_cond_load_relaxed_timeout()

This commit introduces an optimized cpu_poll_relax() for ARM64 that uses
__cmpwait_relaxed() to wait for a value change. It gates this logic on
arch_timer_evtstrm_available() being true to avoid blocking forever without
periodic wakeups from the event stream.

> diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
> --- a/arch/arm64/include/asm/barrier.h
> +++ b/arch/arm64/include/asm/barrier.h

[ ... ]

> +/* Re-declared here to avoid include dependency. */
> +extern bool arch_timer_evtstrm_available(void);
> +
> +/*
> + * In the common case, cpu_poll_relax() sits waiting in __cmpwait_relaxed()
> + * for @ptr value to change.
> + *
> + * State this by defining CPU_POLL_RELAX_WAITS which enables a time-check
> + * optimization in smp_cond_load_{relaxed,acquire}_timeout().
> + */
> +#define CPU_POLL_RELAX_WAITS
> +
> +#define cpu_poll_relax(ptr, val, timeout_ns) do {			\
> +	if (arch_timer_evtstrm_available())				\
> +		__cmpwait_relaxed(ptr, val);				\
> +	else								\
> +		cpu_relax();						\
> +} while (0)

[Severity: Low]
Will this cause a module linkage failure if a loadable kernel module
uses smp_cond_load_relaxed_timeout() or similar APIs?

Since cpu_poll_relax() is a macro, it expands directly in the caller's
code. However, looking at drivers/clocksource/arm_arch_timer.c, it appears
that arch_timer_evtstrm_available() is not exported to loadable modules:

drivers/clocksource/arm_arch_timer.c:arch_timer_evtstrm_available() {
        /*
         * We might get called from a preemptible context.
         ...
}

Without an EXPORT_SYMBOL declaration, any loadable module utilizing this
polling macro will fail to link with an unknown symbol error. Should
arch_timer_evtstrm_available be exported to support loadable modules?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260831202251.305046-1-ankur.a.arora@oracle.com?part=2