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=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 36B89C37121 for ; Mon, 21 Jan 2019 20:15:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0CD6A20861 for ; Mon, 21 Jan 2019 20:15:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728346AbfAUUPT (ORCPT ); Mon, 21 Jan 2019 15:15:19 -0500 Received: from mx2.suse.de ([195.135.220.15]:55672 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727882AbfAUUPT (ORCPT ); Mon, 21 Jan 2019 15:15:19 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id EA8EFAFFD; Mon, 21 Jan 2019 20:15:16 +0000 (UTC) From: Roman Penyaev Cc: Roman Penyaev , Andrew Morton , Davidlohr Bueso , Jason Baron , Al Viro , "Paul E. McKenney" , Linus Torvalds , Andrea Parri , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [RFC PATCH v2 11/13] epoll: support polling from userspace for ep_poll() Date: Mon, 21 Jan 2019 21:14:54 +0100 Message-Id: <20190121201456.28338-12-rpenyaev@suse.de> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20190121201456.28338-1-rpenyaev@suse.de> References: <20190121201456.28338-1-rpenyaev@suse.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit To: unlisted-recipients:; (no To-header on input) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Rule of thumb for epfd polled from userspace is simple: epfd has events if ->head != ->tail, no traversing of each item is performed. Signed-off-by: Roman Penyaev Cc: Andrew Morton Cc: Davidlohr Bueso Cc: Jason Baron Cc: Al Viro Cc: "Paul E. McKenney" Cc: Linus Torvalds Cc: Andrea Parri Cc: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org --- fs/eventpoll.c | 68 ++++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 58 insertions(+), 10 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 3c3721c315a7..e70d1ab64ec1 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -440,6 +440,12 @@ static inline bool ep_polled_by_user(struct eventpoll *ep) return !!ep->user_header; } +static inline bool ep_uring_events_available(struct eventpoll *ep) +{ + return ep_polled_by_user(ep) && + ep->user_header->head != ep->user_header->tail; +} + /** * ep_events_available - Checks if ready events might be available. * @@ -451,7 +457,8 @@ static inline bool ep_polled_by_user(struct eventpoll *ep) static inline int ep_events_available(struct eventpoll *ep) { return !list_empty_careful(&ep->rdllist) || - READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR; + READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR || + ep_uring_events_available(ep); } #ifdef CONFIG_NET_RX_BUSY_POLL @@ -1160,7 +1167,7 @@ static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, int depth) { - struct eventpoll *ep; + struct eventpoll *ep, *tep; bool locked; pt->_key = epi->event.events; @@ -1169,6 +1176,26 @@ static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, ep = epi->ffd.file->private_data; poll_wait(epi->ffd.file, &ep->poll_wait, pt); + + tep = epi->ffd.file->private_data; + if (ep_polled_by_user(tep)) { + /* + * The behaviour differs comparing to full scan of ready + * list for original epoll. If descriptor is pollable + * from userspace we don't do scan of all ready user items: + * firstly because we can't do reverse search of epi by + * uitem bit, secondly this is simply waste of time for + * edge triggered descriptors (user code should be prepared + * to deal with EAGAIN returned from read() or write() on + * inserted file descriptor) and thirdly once event is put + * into user index ring do not touch it from kernel, what + * we do is mark it as EPOLLREMOVED on ep_remove() and + * that's it. + */ + return ep_uring_events_available(tep) ? + EPOLLIN | EPOLLRDNORM : 0; + } + locked = pt && (pt->_qproc == ep_ptable_queue_proc); return ep_scan_ready_list(epi->ffd.file->private_data, @@ -1211,6 +1238,12 @@ static __poll_t ep_eventpoll_poll(struct file *file, poll_table *wait) /* Insert inside our poll wait queue */ poll_wait(file, &ep->poll_wait, wait); + if (ep_polled_by_user(ep)) { + /* Please read detailed comments inside ep_item_poll() */ + return ep_uring_events_available(ep) ? + EPOLLIN | EPOLLRDNORM : 0; + } + /* * Proceed to find out if wanted events are really available inside * the ready list. @@ -2232,6 +2265,8 @@ static int ep_send_events(struct eventpoll *ep, { struct ep_send_events_data esed; + WARN_ON(ep_polled_by_user(ep)); + esed.maxevents = maxevents; esed.events = events; @@ -2278,6 +2313,12 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, lockdep_assert_irqs_enabled(); + if (ep_polled_by_user(ep)) { + if (ep_uring_events_available(ep)) + /* Firstly all events from ring have to be consumed */ + return -ESTALE; + } + if (timeout > 0) { struct timespec64 end_time = ep_set_mstimeout(timeout); @@ -2366,14 +2407,21 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, __set_current_state(TASK_RUNNING); send_events: - /* - * Try to transfer events to user space. In case we get 0 events and - * there's still timeout left over, we go trying again in search of - * more luck. - */ - if (!res && eavail && - !(res = ep_send_events(ep, events, maxevents)) && !timed_out) - goto fetch_events; + if (!res && eavail) { + if (!ep_polled_by_user(ep)) { + /* + * Try to transfer events to user space. In case we get + * 0 events and there's still timeout left over, we go + * trying again in search of more luck. + */ + res = ep_send_events(ep, events, maxevents); + if (!res && !timed_out) + goto fetch_events; + } else { + /* User has to deal with the ring himself */ + res = -ESTALE; + } + } if (waiter) { spin_lock_irq(&ep->wq.lock); -- 2.19.1