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

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Message-ID: <CAJNi4rO5imFOrY-uXGGdEQ45whcOfRoyLtgYqW_s9mOVTpomCA@mail.gmail.com>
Date: Sat, 29 Jun 2024 13:38:56 +0800
From: richard clark <richard.xnu.clark@...il.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
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 9:13 PM Russell King (Oracle)
<linux@...linux.org.uk> wrote:
>
> 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.
>
Ah, you're right. Indeed it's pasted improperly, pls ignore it peacefully :)
>
> 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!
>
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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