linux-kernel - [tip: x86/urgent] x86/aperfmperf: Fix deadlock on cpu_hotplug

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Message-ID: <172226106647.2215.11540272455140168074.tip-bot2@tip-bot2>
Date: Mon, 29 Jul 2024 13:51:06 -0000
From: "tip-bot2 for Jonathan Cameron" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>,
 Thomas Gleixner <tglx@...utronix.de>,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 "Borislav Petkov (AMD)" <bp@...en8.de>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/aperfmperf: Fix deadlock on cpu_hotplug_lock

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     0f7ced7d620ecc7a986843d6aeec41cce3116f41
Gitweb:        https://git.kernel.org/tip/0f7ced7d620ecc7a986843d6aeec41cce3116f41
Author:        Jonathan Cameron <Jonathan.Cameron@...wei.com>
AuthorDate:    Mon, 29 Jul 2024 11:55:04 +01:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Mon, 29 Jul 2024 15:32:37 +02:00

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: c1385c1f0ba3 ("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: Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
Tested-by: Borislav Petkov (AMD) <bp@...en8.de>
Link: https://lore.kernel.org/r/20240729105504.2170-1-Jonathan.Cameron@huawei.com
---
 arch/x86/kernel/cpu/aperfmperf.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c
index b3fa61d..0b69bfb 100644
--- a/arch/x86/kernel/cpu/aperfmperf.c
+++ b/arch/x86/kernel/cpu/aperfmperf.c
@@ -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);
 }
@@ -323,8 +323,10 @@ 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)