From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 38CBEC433FE for ; Fri, 24 Sep 2021 11:04:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1C8D261241 for ; Fri, 24 Sep 2021 11:04:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244606AbhIXLGB (ORCPT ); Fri, 24 Sep 2021 07:06:01 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:41368 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244510AbhIXLGA (ORCPT ); Fri, 24 Sep 2021 07:06:00 -0400 From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1632481466; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=R0xmbt7Av+GwVclLZhRHdpujH9c0cVpxkWZDFBaxUtM=; b=OsU5VzNgLGtvscowoSnpo57k/J92eaphSGiTNWv8fOkgM9kvbwSbg3BzhDg5z2shi90pF7 sx8bFGSIY/PLP/Pm4QOwON/6l9t8NQwzid0k8fbAs4/ZsaOz4MsvpjKkt1u98P7za/S7Dd cVEJbdAtNnSrfv3qVySmTASvY4yKUiqn8Zs49FxlYx/DIc+5tO6tna0q9GqRZ+a5iweaEt ufZHJxBR1M1K3Os9x8r5wSL8xobVsMh8hcUrXwuMoSihqtLPAZie0AXMbe7NgjytJO7ie3 MkIbp0v63kSbVe/jxLfqRmDcHh8/2fCDIoMmf2Dy+hbXYVT0fFISwAupCo88RQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1632481466; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=R0xmbt7Av+GwVclLZhRHdpujH9c0cVpxkWZDFBaxUtM=; b=ADW+qoGHk4FKZa85mQXSXh5rJDACF1IJmkDonEbagVzDoaNlHD9Bf0S5UTGdfeByEe4oy1 H4oboX/eR8q281Ag== To: Sohil Mehta , x86@kernel.org Cc: Sohil Mehta , Tony Luck , Dave Hansen , Ingo Molnar , Borislav Petkov , "H . Peter Anvin" , Andy Lutomirski , Jens Axboe , Christian Brauner , Peter Zijlstra , Shuah Khan , Arnd Bergmann , Jonathan Corbet , Ashok Raj , Jacob Pan , Gayatri Kammela , Zeng Guang , Dan Williams , Randy E Witt , Ravi V Shankar , Ramesh Thomas , linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [RFC PATCH 11/13] x86/uintr: Introduce uintr_wait() syscall In-Reply-To: <20210913200132.3396598-12-sohil.mehta@intel.com> References: <20210913200132.3396598-1-sohil.mehta@intel.com> <20210913200132.3396598-12-sohil.mehta@intel.com> Date: Fri, 24 Sep 2021 13:04:25 +0200 Message-ID: <87r1dedykm.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Mon, Sep 13 2021 at 13:01, Sohil Mehta wrote: > Add a new system call to allow applications to block in the kernel and > wait for user interrupts. > > blocking system calls like sleep(), read(), epoll(), etc. > > uintr_wait() is a placeholder syscall while we decide on that > behaviour.> > > When the application makes this syscall the notification vector is > switched to a new kernel vector. Any new SENDUIPI will invoke the kernel > interrupt which is then used to wake up the process. > > Currently, the task wait list is global one. To make the implementation > scalable there is a need to move to a distributed per-cpu wait list. How are per cpu wait lists going to solve the problem? > + > +/* > + * Handler for UINTR_KERNEL_VECTOR. > + */ > +DEFINE_IDTENTRY_SYSVEC(sysvec_uintr_kernel_notification) > +{ > + /* TODO: Add entry-exit tracepoints */ > + ack_APIC_irq(); > + inc_irq_stat(uintr_kernel_notifications); > + > + uintr_wake_up_process(); So this interrupt happens for any of those notifications. How are they differentiated? > > +int uintr_receiver_wait(void) > +{ > + struct uintr_upid_ctx *upid_ctx; > + unsigned long flags; > + > + if (!is_uintr_receiver(current)) > + return -EOPNOTSUPP; > + > + upid_ctx = current->thread.ui_recv->upid_ctx; > + upid_ctx->upid->nc.nv = UINTR_KERNEL_VECTOR; > + upid_ctx->waiting = true; > + spin_lock_irqsave(&uintr_wait_lock, flags); > + list_add(&upid_ctx->node, &uintr_wait_list); > + spin_unlock_irqrestore(&uintr_wait_lock, flags); > + > + set_current_state(TASK_INTERRUPTIBLE); Because we have not enough properly implemented wait primitives you need to open code one which is blantantly wrong vs. a concurrent wake up? > + schedule(); How is that correct vs. a spurious wakeup? What takes care that the entry is removed from the list? Again. We have proper wait primitives. > + return -EINTR; > +} > + > +/* > + * Runs in interrupt context. > + * Scan through all UPIDs to check if any interrupt is on going. > + */ > +void uintr_wake_up_process(void) > +{ > + struct uintr_upid_ctx *upid_ctx, *tmp; > + unsigned long flags; > + > + spin_lock_irqsave(&uintr_wait_lock, flags); > + list_for_each_entry_safe(upid_ctx, tmp, &uintr_wait_list, node) { > + if (test_bit(UPID_ON, (unsigned long*)&upid_ctx->upid->nc.status)) { > + set_bit(UPID_SN, (unsigned long *)&upid_ctx->upid->nc.status); > + upid_ctx->upid->nc.nv = UINTR_NOTIFICATION_VECTOR; > + upid_ctx->waiting = false; > + wake_up_process(upid_ctx->task); > + list_del(&upid_ctx->node); So any of these notification interrupts does a global mass wake up? How does that make sense? > + } > + } > + spin_unlock_irqrestore(&uintr_wait_lock, flags); > +} > + > +/* Called when task is unregistering/exiting */ > +static void uintr_remove_task_wait(struct task_struct *task) > +{ > + struct uintr_upid_ctx *upid_ctx, *tmp; > + unsigned long flags; > + > + spin_lock_irqsave(&uintr_wait_lock, flags); > + list_for_each_entry_safe(upid_ctx, tmp, &uintr_wait_list, node) { > + if (upid_ctx->task == task) { > + pr_debug("wait: Removing task %d from wait\n", > + upid_ctx->task->pid); > + upid_ctx->upid->nc.nv = UINTR_NOTIFICATION_VECTOR; > + upid_ctx->waiting = false; > + list_del(&upid_ctx->node); > + } What? You have to do a global list walk to find the entry which you added yourself? Thanks, tglx