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Tue, 03 Jun 2025 19:31:08 -0700 (PDT) From: Yunhui Cui To: rafael@kernel.org, lenb@kernel.org, Pierre.Gondois@arm.com, viresh.kumar@linaro.org, sudeep.holla@arm.com, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Yunhui Cui , Xu Lu Subject: [PATCH] ACPI: CPPC: Fix panic caused by NULL pointer dereference Date: Wed, 4 Jun 2025 10:30:36 +0800 Message-Id: <20250604023036.99553-1-cuiyunhui@bytedance.com> X-Mailer: git-send-email 2.39.2 (Apple Git-143) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" With nosmp in cmdline, other CPUs are not brought up, leaving their cpc_desc_ptr NULL. CPU0's iteration via for_each_possible_cpu() dereferences these NULL pointers, causing panic. Panic backtrace: [ 0.401123] Unable to handle kernel NULL pointer dereference at virtual = address 00000000000000b8 ... [ 0.403255] [] cppc_allow_fast_switch+0x6a/0xd4 ... Kernel panic - not syncing: Attempted to kill init! Fixes: 3cc30dd00a58 ("cpufreq: CPPC: Enable fast_switch") Reported-by: Xu Lu Signed-off-by: Yunhui Cui --- drivers/acpi/cppc_acpi.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c index a9ae2fd628630..6b649031808f8 100644 --- a/drivers/acpi/cppc_acpi.c +++ b/drivers/acpi/cppc_acpi.c @@ -476,7 +476,7 @@ bool cppc_allow_fast_switch(void) struct cpc_desc *cpc_ptr; int cpu; =20 - for_each_possible_cpu(cpu) { + for_each_present_cpu(cpu) { cpc_ptr =3D per_cpu(cpc_desc_ptr, cpu); desired_reg =3D &cpc_ptr->cpc_regs[DESIRED_PERF]; if (!CPC_IN_SYSTEM_MEMORY(desired_reg) && --=20 2.39.5