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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 096DDC433F5 for ; Fri, 21 Jan 2022 15:19:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351313AbiAUPTS (ORCPT ); Fri, 21 Jan 2022 10:19:18 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55904 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351337AbiAUPTO (ORCPT ); Fri, 21 Jan 2022 10:19:14 -0500 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 24711C06173B; Fri, 21 Jan 2022 07:19:14 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=ApWlAhGVn9PnMXNrJHt7gtCR31r9LK5mSVjYiz9qbVc=; b=dB7pkf5xgvL8JqzBxZV7AwA+Zy vdfTp734SREq/U3hYDd9Q/sBd0koUEWpk9iO5Qx7RLXpYua9nmzkTlMwPN1q/ZNL5Puya3OGkUk1X x5uOyr/uma6z/4nnft7NFTCfjVljHcrSXMDoxlUNQNlC9ERC0nDZECbRN/3klhbmX3aV2U34u2/tj U7e5XE0J7KQ0fkKaPfYj4xjUOL7PFW2kj9iZ5y4cRV8ofZj8xfgqzOQ75By4lXQDTiMmapgt1pb1u crpRPhPuu1uCdhB1Ush2xcTOC3ZcDWS7P5K3HVAti1IbBmJYliHUeadZ02cO5RfNbD7lYvDW49xTT CE1kbowA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1nAvgd-002bJm-NE; Fri, 21 Jan 2022 15:18:48 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 063E49867E1; Fri, 21 Jan 2022 16:18:46 +0100 (CET) Date: Fri, 21 Jan 2022 16:18:45 +0100 From: Peter Zijlstra To: mingo@redhat.com, tglx@linutronix.de, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org, x86@kernel.org, pjt@google.com, posk@google.com, avagin@google.com, jannh@google.com, tdelisle@uwaterloo.ca, mark.rutland@arm.com, posk@posk.io Subject: Re: [RFC][PATCH v2 5/5] sched: User Mode Concurency Groups Message-ID: <20220121151845.GB22849@worktop.programming.kicks-ass.net> References: <20220120155517.066795336@infradead.org> <20220120160822.914418096@infradead.org> <20220121114758.GF20638@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220121114758.GF20638@worktop.programming.kicks-ass.net> Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Fri, Jan 21, 2022 at 12:47:58PM +0100, Peter Zijlstra wrote: > On Thu, Jan 20, 2022 at 04:55:22PM +0100, Peter Zijlstra wrote: > > > +SYSCALL_DEFINE2(umcg_wait, u32, flags, u64, timo) > > +{ > > + struct task_struct *tsk = current; > > + struct umcg_task __user *self = READ_ONCE(tsk->umcg_task); > > + bool worker = tsk->flags & PF_UMCG_WORKER; > > + int ret; > > + > > + if (!self || flags) > > + return -EINVAL; > > + > > + if (worker) { > > + tsk->flags &= ~PF_UMCG_WORKER; > > + if (timo) > > + return -ERANGE; > > + } > > + > > + /* see umcg_sys_{enter,exit}() syscall exceptions */ > > + ret = umcg_pin_pages(); > > + if (ret) > > + goto unblock; > > + > > + /* > > + * Clear UMCG_TF_COND_WAIT *and* check state == RUNNABLE. > > + */ > > + ret = umcg_update_state(tsk, self, UMCG_TASK_RUNNABLE, UMCG_TASK_RUNNABLE); > > + if (ret) > > + goto unpin; > > + > > + ret = umcg_wake_next(tsk, self); > > + if (ret) > > + goto unpin; > > + > > + if (worker) { > > + /* > > + * If this fails it is possible ::next_tid is already running > > + * while this task is not going to block. This violates our > > + * constraints. > > + * > > + * That said, pretty much the only way to make this fail is by > > + * force munmap()'ing things. In which case one is most welcome > > + * to the pieces. > > + */ > > + ret = umcg_enqueue_and_wake(tsk); > > + if (ret) > > + goto unpin; > > + } > > + > > + umcg_unpin_pages(); > > + > > + ret = umcg_wait(timo); > > + switch (ret) { > > + case 0: /* all done */ > > + case -EINTR: /* umcg_notify_resume() will continue the wait */ > > So I was playing with the whole worker timeout thing last night and > realized this is broken. If we get a signal while we have a timeout, the > timeout gets lost. > > I think the easiest solution is to have umcg_notify_resume() also resume > the timeout, but the first pass of that was yuck, so I need to try > again. Something like this, still yuck though. Also still need to write me a test for this. --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1300,12 +1300,14 @@ struct task_struct { clockid_t umcg_clock; struct umcg_task __user *umcg_task; - /* setup by umcg_pin_enter() */ + /* setup by umcg_pin_pages() */ struct page *umcg_page; struct task_struct *umcg_server; struct umcg_task __user *umcg_server_task; struct page *umcg_server_page; + + u64 umcg_timeout; #endif struct tlbflush_unmap_batch tlb_ubc; --- a/kernel/sched/umcg.c +++ b/kernel/sched/umcg.c @@ -232,6 +232,8 @@ static int umcg_update_state(struct task /* Called from syscall enter path and exceptions that can schedule */ void umcg_sys_enter(struct pt_regs *regs, long syscall) { + current->umcg_timeout = 0; + /* avoid recursion vs our own syscalls */ if (syscall == __NR_umcg_wait || syscall == __NR_umcg_ctl) @@ -519,6 +521,7 @@ void umcg_notify_resume(struct pt_regs * struct umcg_task __user *self = tsk->umcg_task; bool worker = tsk->flags & PF_UMCG_WORKER; u32 state; + int ret; /* avoid recursion vs schedule() */ if (worker) @@ -554,12 +557,17 @@ void umcg_notify_resume(struct pt_regs * umcg_unpin_pages(); } - switch (umcg_wait(0)) { + ret = umcg_wait(tsk->umcg_timeout); + switch (ret) { case 0: case -EINTR: /* we will resume the wait after the signal */ break; + case -ETIMEDOUT: + regs_set_return_value(regs, ret); + break; + default: UMCG_DIE("wait"); } @@ -759,6 +767,7 @@ SYSCALL_DEFINE2(umcg_wait, u32, flags, u switch (ret) { case 0: /* all done */ case -EINTR: /* umcg_notify_resume() will continue the wait */ + tsk->umcg_timeout = timo; ret = 0; break;