linux-kernel - [PATCH] cpu: fix hard lockup triggered by printk calls within scheduling context

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Message-ID: <20250924123247.807-1-shechenglong@xfusion.com>
Date: Wed, 24 Sep 2025 20:32:47 +0800
From: shechenglong <shechenglong@...sion.com>
To: <catalin.marinas@....com>
CC: <will@...nel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <stone.xulei@...sion.com>,
	<chenjialong@...sion.com>, <yuxiating@...sion.com>, shechenglong
	<shechenglong@...sion.com>, Mark Rutland <mark.rutland@....com>
Subject: [PATCH] cpu: fix hard lockup triggered by printk calls within scheduling context

relocate the printk() calls from spectre_v4_mitigations_off() and
spectre_v2_mitigations_off() into setup_system_capabilities() function,
preventing hard lockups that occur when printk() is invoked from scheduler context.

Link: https://patchwork.kernel.org/project/linux-arm-kernel/patch/20250918064907.1832-1-shechenglong@xfusion.com/
Suggested-by: Mark Rutland <mark.rutland@....com>
Suggested-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: shechenglong <shechenglong@...sion.com>
---
 arch/arm64/include/asm/spectre.h |  3 +++
 arch/arm64/kernel/cpufeature.c   |  9 +++++++++
 arch/arm64/kernel/proton-pack.c  | 18 ++++--------------
 3 files changed, 16 insertions(+), 14 deletions(-)

diff --git a/arch/arm64/include/asm/spectre.h b/arch/arm64/include/asm/spectre.h
index 8fef12626090..6fe29df41788 100644
--- a/arch/arm64/include/asm/spectre.h
+++ b/arch/arm64/include/asm/spectre.h
@@ -118,5 +118,8 @@ void spectre_bhb_patch_wa3(struct alt_instr *alt,
 void spectre_bhb_patch_clearbhb(struct alt_instr *alt,
 				__le32 *origptr, __le32 *updptr, int nr_inst);
 
+bool spectre_v2_mitigations_off(void);
+bool spectre_v4_mitigations_off(void);
+
 #endif	/* __ASSEMBLY__ */
 #endif	/* __ASM_SPECTRE_H */
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index ef269a5a37e1..7d1f541e66a0 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -94,6 +94,7 @@
 #include <asm/traps.h>
 #include <asm/vectors.h>
 #include <asm/virt.h>
+#include <asm/spectre.h>
 
 /* Kernel representation of AT_HWCAP and AT_HWCAP2 */
 static DECLARE_BITMAP(elf_hwcap, MAX_CPU_FEATURES) __read_mostly;
@@ -3942,6 +3943,14 @@ static void __init setup_system_capabilities(void)
 	 */
 	if (system_uses_ttbr0_pan())
 		pr_info("emulated: Privileged Access Never (PAN) using TTBR0_EL1 switching\n");
+
+	/*
+	 * Report Spectre mitigations status.
+	 */
+	if (spectre_v2_mitigations_off())
+		pr_info("spectre-v2 mitigation disabled by command line option\n");
+	if (spectre_v4_mitigations_off())
+		pr_info("spectre-v4 mitigation disabled by command-line option\n");
 }
 
 void __init setup_system_features(void)
diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
index edf1783ffc81..0d4a8a123e07 100644
--- a/arch/arm64/kernel/proton-pack.c
+++ b/arch/arm64/kernel/proton-pack.c
@@ -89,14 +89,9 @@ static int __init parse_spectre_v2_param(char *str)
 }
 early_param("nospectre_v2", parse_spectre_v2_param);
 
-static bool spectre_v2_mitigations_off(void)
+bool spectre_v2_mitigations_off(void)
 {
-	bool ret = __nospectre_v2 || cpu_mitigations_off();
-
-	if (ret)
-		pr_info_once("spectre-v2 mitigation disabled by command line option\n");
-
-	return ret;
+	return __nospectre_v2 || cpu_mitigations_off();
 }
 
 static const char *get_bhb_affected_string(enum mitigation_state bhb_state)
@@ -419,15 +414,10 @@ early_param("ssbd", parse_spectre_v4_param);
  * with contradictory parameters. The mitigation is always either "off",
  * "dynamic" or "on".
  */
-static bool spectre_v4_mitigations_off(void)
+bool spectre_v4_mitigations_off(void)
 {
-	bool ret = cpu_mitigations_off() ||
+	return cpu_mitigations_off() ||
 		   __spectre_v4_policy == SPECTRE_V4_POLICY_MITIGATION_DISABLED;
-
-	if (ret)
-		pr_info_once("spectre-v4 mitigation disabled by command-line option\n");
-
-	return ret;
 }
 
 /* Do we need to toggle the mitigation state on entry to/exit from the kernel? */
-- 
2.33.0