Commit 0f7ced7d authored by Jonathan Cameron's avatar Jonathan Cameron Committed by Borislav Petkov (AMD)
Browse files

x86/aperfmperf: Fix deadlock on cpu_hotplug_lock 

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: c1385c1f ("ACPI: processor: Simplify initial onlining to use same path for cold and hotplug")
Closes: https://lore.kernel.org/all/CABXGCsPvqBfL5hQDOARwfqasLRJ_eNPBbCngZ257HOe=xbWDkA@mail.gmail.com/


Reported-by: default avatarMikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Suggested-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarJonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Tested-by: default avatarMikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Tested-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240729105504.2170-1-Jonathan.Cameron@huawei.com
parent 8400291e

arch/x86/kernel/cpu/aperfmperf.c

+4 −2
Original line number Diff line number Diff line
@@ -306,7 +306,7 @@ static void freq_invariance_enable(void) 
		WARN_ON_ONCE(1);

		return;

	}

	static_branch_enable(&arch_scale_freq_key);

	static_branch_enable_cpuslocked(&arch_scale_freq_key);

	register_freq_invariance_syscore_ops();

	pr_info("Estimated ratio of average max frequency by base frequency (times 1024): %llu\n", arch_max_freq_ratio);

}
@@ -323,9 +323,11 @@ static void __init bp_init_freq_invariance(void) 
	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)

		return;



	if (intel_set_max_freq_ratio())

	if (intel_set_max_freq_ratio()) {

		guard(cpus_read_lock)();

		freq_invariance_enable();

	}

}



static void disable_freq_invariance_workfn(struct work_struct *work)

{