From nobody Mon Feb 9 14:22:59 2026 Received: from mail.loongson.cn (mail.loongson.cn [114.242.206.163]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 429462AE96; Fri, 9 May 2025 02:06:38 +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=1746756402; cv=none; b=XZmfO0p6DzPkKDdavD9hRxj5Fp8/xtD1HZEpQlcPOZZd3upvwr+FNP95qWXLwdlQHi+pXrBvfBbzmUp83SrtC/pWAyZ+PdoxsxC0cdyej//W8MTGdjNgHvycZQWkjyld6Nl7LwpgMX9sXsaEp7bLpGaunPDgFPtZCZX07QbmPRU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746756402; c=relaxed/simple; bh=eOG+6uPAgB6kk87jbQU1jozNIa3ia4nGj0etd0Lgu8Y=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=qR/O+i8XR+6f7IPb0E+AF9IsbquFzsFDPq4oWGkZn473d8OreZGu2OS4QBL/zoY/nUPQaJbF9/vv7dH41tYja39wfcenTCB4OewlGR2Q/Pgu12oJveTnBC27kemnyjV7O+/QWJRTAzX3W5qyBPx5tM3mt2ssoedumXXCXhHXgjk= 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 _____8BxjawlYx1oktPaAA--.63242S3; Fri, 09 May 2025 10:06:29 +0800 (CST) Received: from localhost.localdomain (unknown [10.2.10.34]) by front1 (Coremail) with SMTP id qMiowMBxLscjYx1owBG_AA--.32426S2; Fri, 09 May 2025 10:06:27 +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 , stable@vger.kernel.org, Huacai Chen Subject: [PATCH] LoongArch: Prevent cond_resched() occurring within kernel-fpu Date: Fri, 9 May 2025 10:06:26 +0800 Message-Id: <20250509020626.23414-1-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: qMiowMBxLscjYx1owBG_AA--.32426S2 X-CM-SenderInfo: x2kd0wxwld05hdqjqz5rrqw2lrqou0/ X-Coremail-Antispam: 1Uk129KBj93XoW7uryUKFyDXFyxuryDtr15WrX_yoW5Jr4Upr yfur95tr4UJa4ava9rJw18Cry5Awn7G34xWa9xG34rA34Yqr18Xwn29r12qF12vFyIyFyS vFnYqrWI93W5A3cCm3ZEXasCq-sJn29KB7ZKAUJUUUU7529EdanIXcx71UUUUU7KY7ZEXa sCq-sGcSsGvfJ3Ic02F40EFcxC0VAKzVAqx4xG6I80ebIjqfuFe4nvWSU5nxnvy29KBjDU 0xBIdaVrnRJUUUB0b4IE77IF4wAFF20E14v26r1j6r4UM7CY07I20VC2zVCF04k26cxKx2 IYs7xG6rWj6s0DM7CIcVAFz4kK6r1Y6r17M28lY4IEw2IIxxk0rwA2F7IY1VAKz4vEj48v e4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Xr0_Ar1l84ACjcxK6xIIjxv20xvEc7CjxVAFwI 0_Gr0_Cr1l84ACjcxK6I8E87Iv67AKxVWxJr0_GcWl84ACjcxK6I8E87Iv6xkF7I0E14v2 6rxl6s0DM2kKe7AKxVWUXVWUAwAS0I0E0xvYzxvE52x082IY62kv0487Mc804VCY07AIYI kI8VC2zVCFFI0UMc02F40EFcxC0VAKzVAqx4xG6I80ewAv7VC0I7IYx2IY67AKxVWUAVWU twAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFVCjc4AY6r1j6r4UM4x0Y48IcxkI7VAKI4 8JMxkF7I0En4kS14v26r126r1DMxAIw28IcxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j 6r4UMxCIbckI1I0E14v26r1Y6r17MI8I3I0E5I8CrVAFwI0_Jr0_Jr4lx2IqxVCjr7xvwV AFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUtVW8ZwCIc40Y0x0EwIxGrwCI42IY6xIIjxv2 0xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x0267AKxVWUJVW8JwCI42IY6xAIw20EY4 v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAFwI0_Jr0_Gr1lIxAIcVC2z280aVCY1x0267AK xVWUJVW8JbIYCTnIWIevJa73UjIFyTuYvjxUcpBTUUUUU Content-Type: text/plain; charset="utf-8" When CONFIG_PREEMPT_COUNT is not configured (i.e. CONFIG_PREEMPT_NONE/ CONFIG_PREEMPT_VOLUNTARY), preempt_disable() / preempt_enable() merely acts as a barrier(). However, in these cases cond_resched() can still trigger a context switch and modify the CSR.EUEN, resulting in do_fpu() exception being activated within the kernel-fpu critical sections, 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 commit d021985 (x86/fpu: Improve crypto performance by making kernel-mode FPU reliably usable in softirqs). It uses local_bh_disable() instead of preempt_disable() for non-RT kernels so it can avoid the cond_resched() issue, and also extend the kernel-fpu application scenarios to the softirq context. Cc: stable@vger.kernel.org Signed-off-by: Tianyang Zhang Signed-off-by: Huacai Chen --- 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..4e469b021cf4 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 fpregs_lock(void) +{ + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + local_bh_disable(); + else + preempt_disable(); +} + +static inline void fpregs_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()) + fpregs_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()) + fpregs_unlock(); } EXPORT_SYMBOL_GPL(kernel_fpu_end); =20 --=20 2.20.1