From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from va-1-113.ptr.blmpb.com (va-1-113.ptr.blmpb.com [209.127.230.113]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BDAD83F6601 for ; Tue, 9 Jun 2026 09:18:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.127.230.113 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780996717; cv=none; b=G9+8C87w4DF0BaxC3nOHBIRLfgfhvUqI62z1+9w5zz8U/Pz6gEDZXKaUIClkAbQ6NX8kJ0pXX5vfFZwkVOBcE7aVSjVShnMEoFDVQkQqhqRXUyivPSor/XxarxfT+qH23heWAMftcr3go1MfAIab26zcuCl44MoAmh6NJtfNxV0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780996717; c=relaxed/simple; bh=DaoCTKAEmmS1xb24C8REU2CZ3tyO1voA8knm3HDbnMY=; h=Cc:From:Date:Message-Id:Subject:Mime-Version:In-Reply-To: Content-Type:To:References; b=TDmBtjGkILxw8zpi/OI8l+CE3fog4l3ny+B5xQ23b6gPW9COitnvfrjclMjgRKquwTGr5vTEONHppGKfJijbvBspmdiGzpy+6ZMhpNUYbSdtv2Zosw8GAptVTIlhpdx7iwbLNqn96lG8Juk8gMqvu3ndXNRIQIGMZtkFAyKzrSg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=bytedance.com; spf=pass smtp.mailfrom=bytedance.com; dkim=pass (2048-bit key) header.d=bytedance.com header.i=@bytedance.com header.b=YrRiuF2a; arc=none smtp.client-ip=209.127.230.113 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=bytedance.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bytedance.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bytedance.com header.i=@bytedance.com header.b="YrRiuF2a" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; s=2212171451; d=bytedance.com; t=1780996710; h=from:subject: mime-version:from:date:message-id:subject:to:cc:reply-to:content-type: mime-version:in-reply-to:message-id; bh=wePV7J6zUH0vCzblJqncGcHwvRMzxtg0nNGmKrGLCi8=; b=YrRiuF2a6AKw/yOZ2cXaTz8g8ibpEsn3ZHpQ9QQobGMjoJsZb1bW1CDvMGilgF+SFhKfyt +b6GrIUwjau5E9iPjFYo21ALZYhIQdZuCpN2g8LE07VIvokkdGfymTqOYzqW/lGQWiKnGL ObSfw1HOy39hmEATjfyjgXPPKpqxyf8eyI8b3FXsd7U79Ig2WtBXz2TzMxEhXpswsS5m9I 51r6MFPI2wpvW5HsedzjyyJUzyxrCG2kBv/gH89QYphcJox/YbdJRYpncf84iRaiHvL7Wt lGWdv/P+C5gX9f6ujrGQEjHXS7ZoQrJAlW/qVdvclNuA0WTMfSEmDfEsThvKsw== X-Mailer: git-send-email 2.20.1 Cc: , "Chuyi Zhou" From: "Chuyi Zhou" Date: Tue, 9 Jun 2026 17:16:59 +0800 Message-Id: <20260609091710.404083-4-zhouchuyi@bytedance.com> X-Original-From: Chuyi Zhou Subject: [PATCH v7 03/14] smp: Refactor remote CPU selection in smp_call_function_any() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 In-Reply-To: <20260609091710.404083-1-zhouchuyi@bytedance.com> Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=UTF-8 To: , , , , , , , , , , , , , X-Lms-Return-Path: References: <20260609091710.404083-1-zhouchuyi@bytedance.com> Currently, smp_call_function_any() disables preemption across the entire process of picking a target CPU, enqueueing the IPI, and synchronously waiting for the remote CPU. Since smp_call_function_single() has already been optimized to re-enable preemption before the synchronous csd_lock_wait(), callers of smp_call_function_any() should also benefit from this optimization to reduce the preemption-disabled critical section. A naive approach would be to simply remove get_cpu() and put_cpu() from smp_call_function_any(), leaving the preemption disablement entirely to smp_call_function_single(). However, doing so opens a dangerous preemption window between picking the remote CPU (e.g., via sched_numa_find_nth_cpu()) and dispatching the IPI inside smp_call_function_single(). If the selected remote CPU is fully offlined during this window, smp_call_function_single() will fail its cpu_online() check and return -ENXIO directly to the caller, violating the guarantee to execute on *any* online CPU in the mask. To safely enable this optimization, this patch refactors the logic of smp_call_function_any() and smp_call_function_single(). By moving the random remote CPU selection into a common __smp_call_function_single(), and keep the entire selection and IPI dispatch process within a single preemption-disabled region. Signed-off-by: Chuyi Zhou Reviewed-by: Sebastian Andrzej Siewior Tested-by: Paul E. McKenney --- kernel/smp.c | 48 ++++++++++++++++++++++++++---------------------- 1 file changed, 26 insertions(+), 22 deletions(-) diff --git a/kernel/smp.c b/kernel/smp.c index 292eefadddbc..9e9dab3b0d51 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -641,17 +641,8 @@ void flush_smp_call_function_queue(void) local_irq_restore(flags); } -/** - * smp_call_function_single - Run a function on a specific CPU - * @cpu: Specific target CPU for this function. - * @func: The function to run. This must be fast and non-blocking. - * @info: An arbitrary pointer to pass to the function. - * @wait: If true, wait until function has completed on other CPUs. - * - * Returns: %0 on success, else a negative status code. - */ -int smp_call_function_single(int cpu, smp_call_func_t func, void *info, - int wait) +static int __smp_call_function_single(int cpu, smp_call_func_t func, + void *info, const struct cpumask *mask, int wait) { call_single_data_t *csd; call_single_data_t csd_stack = { @@ -668,6 +659,14 @@ int smp_call_function_single(int cpu, smp_call_func_t func, void *info, */ this_cpu = get_cpu(); + if (mask) { + /* Try for same CPU (cheapest) */ + if (!cpumask_test_cpu(this_cpu, mask)) + cpu = sched_numa_find_nth_cpu(mask, 0, cpu_to_node(this_cpu)); + else + cpu = this_cpu; + } + /* * Can deadlock when called with interrupts disabled. * We allow cpu's that are not yet online though, as no one else can @@ -712,6 +711,21 @@ int smp_call_function_single(int cpu, smp_call_func_t func, void *info, return err; } + +/** + * smp_call_function_single - Run a function on a specific CPU + * @cpu: Specific target CPU for this function. + * @func: The function to run. This must be fast and non-blocking. + * @info: An arbitrary pointer to pass to the function. + * @wait: If true, wait until function has completed on other CPUs. + * + * Returns: %0 on success, else a negative status code. + */ +int smp_call_function_single(int cpu, smp_call_func_t func, void *info, + int wait) +{ + return __smp_call_function_single(cpu, func, info, NULL, wait); +} EXPORT_SYMBOL(smp_call_function_single); /** @@ -776,17 +790,7 @@ EXPORT_SYMBOL_GPL(smp_call_function_single_async); int smp_call_function_any(const struct cpumask *mask, smp_call_func_t func, void *info, int wait) { - unsigned int cpu; - int ret; - - /* Try for same CPU (cheapest) */ - cpu = get_cpu(); - if (!cpumask_test_cpu(cpu, mask)) - cpu = sched_numa_find_nth_cpu(mask, 0, cpu_to_node(cpu)); - - ret = smp_call_function_single(cpu, func, info, wait); - put_cpu(); - return ret; + return __smp_call_function_single(-1, func, info, mask, wait); } EXPORT_SYMBOL_GPL(smp_call_function_any); -- 2.20.1