From nobody Mon Dec 15 21:57:39 2025 Received: from mail.loongson.cn (mail.loongson.cn [114.242.206.163]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 9EEFCA31 for ; Wed, 7 May 2025 10:06:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=114.242.206.163 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746612393; cv=none; b=LETwS+EsKSrV8386qFrKNrwxmtE4S+j6+TxjRlS5eX80wPP6mZ9uqhwmw3ctdBQpXiwqLMe24bii8LWvZ1EgvfxFRFR5ejYoIRJSeDU1neXmIYqWH/Tzn9MDsAlsVe3zXCNqpRvJwpcy//OTbfh+kb3sSRVmx1Yglw3tbA3ImhI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746612393; c=relaxed/simple; bh=TkYjw2gY1eODfPiUtFnFZw5vNxrfJTGcP3anVqaHl7c=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=gCY7/b0XHY1efySliYl81QyPmun9WEsC77+adR+lB3EbQl0W+SzAvBd/nxiojIbbC0M+rCHgBOfh7dJP2IGIwlFh1mRmLgqli09/50dO/9hCjaiy9Q8uMnVfGEfApvJi9goAycbRxpwh3HlQxswd5b8rOcGOQ+nyteB6/kFKoLw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=loongson.cn; spf=pass smtp.mailfrom=loongson.cn; arc=none smtp.client-ip=114.242.206.163 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=loongson.cn Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=loongson.cn Received: from loongson.cn (unknown [10.2.10.34]) by gateway (Coremail) with SMTP id _____8CxieCjMBtoHwvYAA--.48533S3; Wed, 07 May 2025 18:06:27 +0800 (CST) Received: from localhost.localdomain (unknown [10.2.10.34]) by front1 (Coremail) with SMTP id qMiowMBxXsWiMBtoQcS5AA--.13196S2; Wed, 07 May 2025 18:06:26 +0800 (CST) From: Tianyang Zhang To: chenhuacai@kernel.org, kernel@xen0n.name, bigeasy@linutronix.de, clrkwllms@kernel.org, rostedt@goodmis.org Cc: loongarch@lists.linux.dev, linux-rt-devel@lists.linux.dev, linux-kernel@vger.kernel.org, Tianyang Zhang Subject: [PATCH] Loongarch:Prevent cond_resched occurring within kernel-fpu Date: Wed, 7 May 2025 18:06:24 +0800 Message-Id: <20250507100624.8925-1-zhangtianyang@loongson.cn> X-Mailer: git-send-email 2.20.1 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 X-CM-TRANSID: qMiowMBxXsWiMBtoQcS5AA--.13196S2 X-CM-SenderInfo: x2kd0wxwld05hdqjqz5rrqw2lrqou0/ X-Coremail-Antispam: 1Uk129KBj93XoW7uryrJrW3Cw4rJr1fCF1fKrX_yoW8uF1rpr yS9r95tr4UJ3ZIvay3Jr18Gry5J3ykGw1xWFZxGa4rA3y5Xry8Xwn2gr12qFy29FWIvFWf ZFn5XrWIg3WUA3gCm3ZEXasCq-sJn29KB7ZKAUJUUUUr529EdanIXcx71UUUUU7KY7ZEXa sCq-sGcSsGvfJ3Ic02F40EFcxC0VAKzVAqx4xG6I80ebIjqfuFe4nvWSU5nxnvy29KBjDU 0xBIdaVrnRJUUUBjb4IE77IF4wAFF20E14v26r1j6r4UM7CY07I20VC2zVCF04k26cxKx2 IYs7xG6rWj6s0DM7CIcVAFz4kK6r1Y6r17M28lY4IEw2IIxxk0rwA2F7IY1VAKz4vEj48v e4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_JFI_Gr1l84ACjcxK6xIIjxv20xvEc7CjxVAFwI 0_Jr0_Gr1l84ACjcxK6I8E87Iv67AKxVW0oVCq3wA2z4x0Y4vEx4A2jsIEc7CjxVAFwI0_ GcCE3s1ln4kS14v26r1Y6r17M2AIxVAIcxkEcVAq07x20xvEncxIr21l57IF6xkI12xvs2 x26I8E6xACxx1l5I8CrVACY4xI64kE6c02F40Ex7xfMcIj6xIIjxv20xvE14v26r1Y6r17 McIj6I8E87Iv67AKxVWUJVW8JwAm72CE4IkC6x0Yz7v_Jr0_Gr1lF7xvr2IYc2Ij64vIr4 1lc7CjxVAaw2AFwI0_JF0_Jw1l42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_ Gr1l4IxYO2xFxVAFwI0_Jrv_JF1lx2IqxVAqx4xG67AKxVWUJVWUGwC20s026x8GjcxK67 AKxVWUGVWUWwC2zVAF1VAY17CE14v26r1q6r43MIIYrxkI7VAKI48JMIIF0xvE2Ix0cI8I cVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I0E14v26r1j6r4UMIIF0xvE42xK8VAvwI 8IcIk0rVWUJVWUCwCI42IY6I8E87Iv67AKxVWUJVW8JwCI42IY6I8E87Iv6xkF7I0E14v2 6r1j6r4UYxBIdaVFxhVjvjDU0xZFpf9x07jOa93UUUUU= Content-Type: text/plain; charset="utf-8" When CONFIG_PREEMPT_COUNT is not configured, preempt_disable/preempt_enable merely acts as a barrier. However, cond_resched can still trigger a context switch and modify the EUEN, resulting in do_fpu being activated within kernel-fpu critical section, as demonstrated in the following path: dcn32_calculate_wm_and_dlg DC_FP_START dcn32_calculate_wm_and_dlg_fpu dcn32_find_dummy_latency_index_for_fw_based_mclk_switch dcn32_internal_validate_bw dcn32_enable_phantom_stream dc_create_stream_for_sink kzalloc(GFP_KERNEL) __kmem_cache_alloc_node __cond_resched DC_FP_END This patch is similar to d02198550423a0b695e7a24ec77153209ad45b09 (x86/fpu: Improve crypto performance by making kernel-mode FPU reliably usablein softirqs),to avoids the issue, and extends kernel-fpu application scenarios to softirq. Signed-off-by: Tianyang Zhang --- arch/loongarch/kernel/kfpu.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-) diff --git a/arch/loongarch/kernel/kfpu.c b/arch/loongarch/kernel/kfpu.c index ec5b28e570c9..e60bbaca357a 100644 --- a/arch/loongarch/kernel/kfpu.c +++ b/arch/loongarch/kernel/kfpu.c @@ -18,11 +18,28 @@ static unsigned int euen_mask =3D CSR_EUEN_FPEN; static DEFINE_PER_CPU(bool, in_kernel_fpu); static DEFINE_PER_CPU(unsigned int, euen_current); =20 +static inline void fpu_lock(void) +{ + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + local_bh_disable(); + else + preempt_disable(); +} + +static inline void fpu_unlock(void) +{ + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + local_bh_enable(); + else + preempt_enable(); +} + void kernel_fpu_begin(void) { unsigned int *euen_curr; =20 - preempt_disable(); + if (!irqs_disabled()) + fpu_lock(); =20 WARN_ON(this_cpu_read(in_kernel_fpu)); =20 @@ -73,7 +90,8 @@ void kernel_fpu_end(void) =20 this_cpu_write(in_kernel_fpu, false); =20 - preempt_enable(); + if (!irqs_disabled()) + fpu_unlock(); } EXPORT_SYMBOL_GPL(kernel_fpu_end); =20 --=20 2.20.1