linux-kernel - Re: Will smp_call_function_single(cpu, ...) broadcast IPI to all other cpus?

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Message-ID: <Zn63DQhf9nMLooVw@shell.armlinux.org.uk>
Date: Fri, 28 Jun 2024 14:13:49 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: richard clark <richard.xnu.clark@...il.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, Marc Zyngier <maz@...nel.org>,
	Mark Rutland <mark.rutland@....com>, will@...nel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: Will smp_call_function_single(cpu, ...) broadcast IPI to all
 other cpus?

On Fri, Jun 28, 2024 at 06:21:25PM +0800, richard clark wrote:
> The output is:
> 
>           insmod-1746    [000] dn.h1..   928.400039: ipi_raise:
> target_mask=00000000,000000ffe (Function call interrupts)
>           insmod-1746    [000] dn.h2..   928.400042: <stack trace>
>  => trace_event_raw_event_ipi_raise
>  => smp_cross_call
>  => arch_send_call_function_single_ipi
>  => send_call_function_single_ipi

I'm not sure whether the above is misproperly pasted or not, but if it
is correct, it shows a problem.

We can see from the first line that the target mask covers CPUs 1..11.
However, the call chain is for arch_send_call_function_single_ipi(),
which does:

	smp_cross_call(cpumask_of(cpu), IPI_CALL_FUNC);

and cpumask_of(cpu) should only ever contain a single bit, and not
multiple bits which the output above suggests it does!

-- 
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