linux-kernel - Re: [PATCH] x86/aperfmperf: Fix deadlock on cpu_hotplug

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Message-ID: <87ikwo8m00.ffs@tglx>
Date: Mon, 29 Jul 2024 13:40:15 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>, Mikhail Gavrilov
 <mikhail.v.gavrilov@...il.com>, rafael.j.wysocki@...el.com,
 catalin.marinas@....com, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
 <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 "H . Peter Anvin" <hpa@...or.com>, Terry.bowman@....com
Cc: linuxarm@...wei.com, guohanjun@...wei.com, gshan@...hat.com,
 miguel.luis@...cle.com, Linux List Kernel Mailing
 <linux-kernel@...r.kernel.org>, Linux regressions mailing list
 <regressions@...ts.linux.dev>, shameerali.kolothum.thodi@...wei.com
Subject: Re: [PATCH] x86/aperfmperf: Fix deadlock on cpu_hotplug_lock

On Mon, Jul 29 2024 at 11:55, Jonathan Cameron wrote:
> The broken patch results in a call to init_freq_invariance_cppc() in a CPU
> hotplug handler in both the path for initially present CPUs and those
> hotplugged later.  That function includes a one time call to
> amd_set_max_freq_ratio() which in turn calls freq_invariance_enable() that
> has a static_branch_enable() which takes the cpu_hotlug_lock which is
> already held.
>
> Avoid the deadlock by using static_branch_enable_cpuslocked() as the lock
> will always be already held.  The equivalent path on Intel does not
> already hold this lock, so take it around the call to
> freq_invariance_enable(), which results in it being held over the call to
> register_syscall_ops, which looks to be safe to do.
>
> Fixes: c1385c1f0ba3 ("ACPI: processor: Simplify initial onlining to use same path for cold and hotplug")
> Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
> Closes: https://lore.kernel.org/all/CABXGCsPvqBfL5hQDOARwfqasLRJ_eNPBbCngZ257HOe=xbWDkA@mail.gmail.com/
> Suggested-by: Thomas Gleixner <tglx@...utronix.de>
> Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>