From patchwork Mon Nov 28 12:20:06 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Nicolai_H=C3=A4hnle?= X-Patchwork-Id: 9449465 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 5BDE8600CB for ; Mon, 28 Nov 2016 12:20:39 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 4BB6827BE5 for ; Mon, 28 Nov 2016 12:20:39 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 4072127BFF; Mon, 28 Nov 2016 12:20:39 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.1 required=2.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED, DKIM_SIGNED, FREEMAIL_FROM, RCVD_IN_DNSWL_MED, T_DKIM_INVALID autolearn=ham version=3.3.1 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id A33F227BE5 for ; Mon, 28 Nov 2016 12:20:38 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 91EB56E2BD; Mon, 28 Nov 2016 12:20:35 +0000 (UTC) X-Original-To: dri-devel@lists.freedesktop.org Delivered-To: dri-devel@lists.freedesktop.org Received: from mail-wm0-x243.google.com (mail-wm0-x243.google.com [IPv6:2a00:1450:400c:c09::243]) by gabe.freedesktop.org (Postfix) with ESMTPS id 4279C6E2BD for ; Mon, 28 Nov 2016 12:20:28 +0000 (UTC) Received: by mail-wm0-x243.google.com with SMTP id g23so18702059wme.1 for ; Mon, 28 Nov 2016 04:20:28 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=A9tNM8CutjM3wP2EB+/XeqQnIxVkcYLHSeTFGpvx9Bk=; b=ec3xB5hcFFUry376BnV9dYqfPErXeHI+8SOYdr3MaQBmN0+xehP9yBFRjs2HSgpl2Y y3amYN0xZ0rV0mwOIiXu/0gxYxqjq5LK90G3Nt1NQxFSgsLoiptpdxYeebkIUBDz1IWF xmw2hIVUAFvTXGqUKjCXF3Y7VXwz0dMo2rBv+Pt1J1nhvJpb7df5XeHpXlHuNvl5bePp slTfYw1RMUaLJbSCFX9Ia4E9iKFB+MaNPLOqeybUHKI4/bkpPG5y6OEKZQmBFXYT00TK yNuTvhTE8G/yRsFYn/MEyWNaftkqMT+yKihJbteKwLsaMMDQ8Z8xolfQMHujdXCwGja8 kMgA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=A9tNM8CutjM3wP2EB+/XeqQnIxVkcYLHSeTFGpvx9Bk=; b=D52lkAWm/ZSgmk2ITPIi/INWKt6WsnHRtEKaZJYA24qKs+m+CZhzgPJqmSeb74kf0J hgf25hcS/RgeZfjHnVNvCUopHZD4zA2YZX+GPHK6y0808bLAcrIxV81g0KJhKJNihw9T mSzzIfLKx7jHD806BeGWvNW+8/yTLonjzk59D8a9uQAyTKnEoJqPMRSte5NhLRfbmriw PDhOLBX4tYca8BSWvQKTf2OZytkTK+vQQtKoAcrgQnc6PiWUFLALvSF2Dk2iU0ModWq1 6j97y0AbyaOGJEpTx+jzCDUv9T4Cb/WrZ8/WnbjNVG8Il9nQ1/r5tJJLuuq0FoWF/pih oG7w== X-Gm-Message-State: AKaTC02dKxle5a0JReJf1t8C0kaJTXsPwkitKXayfSPpxLqT36PQ8mxcqT5kuDGU9wHqNA== X-Received: by 10.28.170.134 with SMTP id t128mr18099958wme.29.1480335626413; Mon, 28 Nov 2016 04:20:26 -0800 (PST) Received: from cassiopeia.fritz.box ([2001:a61:1119:dc01:d88b:9432:f601:27ed]) by smtp.gmail.com with ESMTPSA id a13sm28830511wma.18.2016.11.28.04.20.25 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 28 Nov 2016 04:20:25 -0800 (PST) From: =?UTF-8?q?Nicolai=20H=C3=A4hnle?= To: linux-kernel@vger.kernel.org Subject: [PATCH 05/11] locking/ww_mutex: Add waiters in stamp order Date: Mon, 28 Nov 2016 13:20:06 +0100 Message-Id: <1480335612-12069-6-git-send-email-nhaehnle@gmail.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1480335612-12069-1-git-send-email-nhaehnle@gmail.com> References: <1480335612-12069-1-git-send-email-nhaehnle@gmail.com> MIME-Version: 1.0 Cc: Maarten Lankhorst , =?UTF-8?q?Nicolai=20H=C3=A4hnle?= , Peter Zijlstra , dri-devel@lists.freedesktop.org, Ingo Molnar X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" X-Virus-Scanned: ClamAV using ClamSMTP From: Nicolai Hähnle Add regular waiters in stamp order. Keep adding waiters that have no context in FIFO order and take care not to starve them. While adding our task as a waiter, back off if we detect that there is a waiter with a lower stamp in front of us. Make sure to call lock_contended even when we back off early. Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Maarten Lankhorst Cc: Daniel Vetter Cc: Chris Wilson Cc: dri-devel@lists.freedesktop.org Signed-off-by: Nicolai Hähnle --- include/linux/mutex.h | 3 ++ kernel/locking/mutex.c | 76 +++++++++++++++++++++++++++++++++++++++++++++----- 2 files changed, 72 insertions(+), 7 deletions(-) diff --git a/include/linux/mutex.h b/include/linux/mutex.h index b97870f..118a3b6 100644 --- a/include/linux/mutex.h +++ b/include/linux/mutex.h @@ -20,6 +20,8 @@ #include #include +struct ww_acquire_ctx; + /* * Simple, straightforward mutexes with strict semantics: * @@ -75,6 +77,7 @@ static inline struct task_struct *__mutex_owner(struct mutex *lock) struct mutex_waiter { struct list_head list; struct task_struct *task; + struct ww_acquire_ctx *ww_ctx; #ifdef CONFIG_DEBUG_MUTEXES void *magic; #endif diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 585627f..01dcae7 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -628,6 +628,40 @@ __ww_mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx) return 0; } +static inline int __sched +__ww_mutex_add_waiter(struct mutex_waiter *waiter, + struct mutex *lock, + struct ww_acquire_ctx *ww_ctx) +{ + if (ww_ctx) { + struct mutex_waiter *cur; + + /* + * Add the waiter before the first waiter with a higher stamp. + * Waiters without a context are skipped to avoid starving + * them. + */ + list_for_each_entry(cur, &lock->wait_list, list) { + if (!cur->ww_ctx) + continue; + + if (__ww_mutex_stamp_after(ww_ctx, cur->ww_ctx)) { + /* Back off immediately if necessary. */ + if (ww_ctx->acquired > 0) + return -EDEADLK; + + continue; + } + + list_add_tail(&waiter->list, &cur->list); + return 0; + } + } + + list_add_tail(&waiter->list, &lock->wait_list); + return 0; +} + /* * Lock a mutex (possibly interruptible), slowpath: */ @@ -677,15 +711,25 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, debug_mutex_lock_common(lock, &waiter); debug_mutex_add_waiter(lock, &waiter, task); - /* add waiting tasks to the end of the waitqueue (FIFO): */ - list_add_tail(&waiter.list, &lock->wait_list); + lock_contended(&lock->dep_map, ip); + + if (!use_ww_ctx) { + /* add waiting tasks to the end of the waitqueue (FIFO): */ + list_add_tail(&waiter.list, &lock->wait_list); + } else { + /* Add in stamp order, waking up waiters that must back off. */ + ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx); + if (ret) + goto err_early_backoff; + + waiter.ww_ctx = ww_ctx; + } + waiter.task = task; if (__mutex_waiter_is_first(lock, &waiter)) __mutex_set_flag(lock, MUTEX_FLAG_WAITERS); - lock_contended(&lock->dep_map, ip); - set_task_state(task, state); for (;;) { /* @@ -693,8 +737,12 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, * mutex_unlock() handing the lock off to us, do a trylock * before testing the error conditions to make sure we pick up * the handoff. + * + * For w/w locks, we always need to do this even if we're not + * currently the first waiter, because we may have been the + * first waiter during the unlock. */ - if (__mutex_trylock(lock, first)) + if (__mutex_trylock(lock, use_ww_ctx || first)) goto acquired; /* @@ -716,7 +764,20 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, spin_unlock_mutex(&lock->wait_lock, flags); schedule_preempt_disabled(); - if (!first && __mutex_waiter_is_first(lock, &waiter)) { + if (use_ww_ctx && ww_ctx) { + /* + * Always re-check whether we're in first position. We + * don't want to spin if another task with a lower + * stamp has taken our position. + * + * We also may have to set the handoff flag again, if + * our position at the head was temporarily taken away. + */ + first = __mutex_waiter_is_first(lock, &waiter); + + if (first) + __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF); + } else if (!first && __mutex_waiter_is_first(lock, &waiter)) { first = true; __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF); } @@ -728,7 +789,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, * or we must see its unlock and acquire. */ if ((first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, true)) || - __mutex_trylock(lock, first)) + __mutex_trylock(lock, use_ww_ctx || first)) break; spin_lock_mutex(&lock->wait_lock, flags); @@ -761,6 +822,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, err: __set_task_state(task, TASK_RUNNING); mutex_remove_waiter(lock, &waiter, task); +err_early_backoff: spin_unlock_mutex(&lock->wait_lock, flags); debug_mutex_free_waiter(&waiter); mutex_release(&lock->dep_map, 1, ip);