From patchwork Tue Nov 15 00:58:59 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Beau Belgrave X-Patchwork-Id: 20114 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:a5d:6687:0:0:0:0:0 with SMTP id l7csp2451273wru; Mon, 14 Nov 2022 17:05:13 -0800 (PST) X-Google-Smtp-Source: AA0mqf42bSpyFnvqqRCi2LLTAjiBZ5WRyA2nqeAEK4dtcENyXnlf7qbrgb088xAvo4txML02j40v X-Received: by 2002:a17:90a:b286:b0:213:34f7:fb14 with SMTP id c6-20020a17090ab28600b0021334f7fb14mr15605121pjr.25.1668474312690; Mon, 14 Nov 2022 17:05:12 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1668474312; cv=none; d=google.com; s=arc-20160816; b=q0ueejduG6kERSES9gxtteYCtUg8fhyoXeeSPhtm3y4HcHssuG6uYhqr73TkzhrpuE ewB3QY238AY/EWmHOWQ8k54EwsBXUpkvM2LHk8AaL/LGKHGQ3a28gIuKIUL9s858ZSgV IxYlEfrmX2099i9/5iqBgb8Z1YsovE4DciMiILurUhZrQOK6s8EAlDLB//OVm04/xHJN HXutI0vcVtO9xTLphA2oKM/3VaMmasM6ixLoJo1ogvexps2XjKq3n8Ox4RFl9+W5xqvO /pwVig2b1duZxuVUx/IP+rhleNgQtSDU+JB4RHS0yyoIRhgP8yPY73VBdyW4yJwueVMe PeuA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:date:subject:cc:to:from :dkim-signature:dkim-filter; bh=n/wvT+9Dns6pzgP7Q76Ub9SkiPIlair3txo81hgTg+E=; b=qFC4iL6nUmCJ0kxnHLX8ujzI0wIuruDUpLdfPnIFH8kWmUkbDqL3pnmLtfeysHuu6q 1x/zAQxZ02zQ2zNBp6PMjraZ7OaMABJls5xPFnHlNT7UyovRU0CrATlOM7eYEtgfnp+Q ZpNNpvSM0Qlxr+xINOMqj/n3yiDwTHvnWlPs4IfH0TEOYqwhXj55cE3GZz2Fa0RtZCBw uZdk3KFwURj6gDeVnst8pNhviXPCntuuZMn8mR8OYP8j4wWS2X0xUJ21eeMdrGq1Lo03 F8+4eu43P0Kxo/WtD98Ug24xnu+wCVxAu0DA1qV9eoDrUu/l3kkIxJfuKEQpK7hRqMlZ ARlw== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@linux.microsoft.com header.s=default header.b=LSQdyPQi; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linux.microsoft.com Received: from out1.vger.email (out1.vger.email. [2620:137:e000::1:20]) by mx.google.com with ESMTP id eb9-20020a056a004c8900b0055fdb74973esi9971175pfb.140.2022.11.14.17.04.57; Mon, 14 Nov 2022 17:05:12 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@linux.microsoft.com header.s=default header.b=LSQdyPQi; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linux.microsoft.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237819AbiKOA7Y (ORCPT + 99 others); Mon, 14 Nov 2022 19:59:24 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50802 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237725AbiKOA7L (ORCPT ); Mon, 14 Nov 2022 19:59:11 -0500 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id DA68ADFDC; Mon, 14 Nov 2022 16:59:08 -0800 (PST) Received: from W11-BEAU-MD.localdomain (unknown [76.135.50.127]) by linux.microsoft.com (Postfix) with ESMTPSA id 6EF5220B83CB; Mon, 14 Nov 2022 16:59:08 -0800 (PST) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 6EF5220B83CB DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1668473948; bh=n/wvT+9Dns6pzgP7Q76Ub9SkiPIlair3txo81hgTg+E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=LSQdyPQiJ6fmcJte0+4selytSxQY6x6QTcY6gmG9aFA5ZLIWSqqEoAgcPWg5Cr+gg 1pVbv4NyEvkz+5L/zgG67VYzpiQbuMDYwn5hj+y/nr5kR8QW8S0+uprJCNHR6RYGBX QwAjbrF9KgJ3aUXW7s4aVvBfhOjcM9u3hmVelveI= From: Beau Belgrave To: rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, dcook@linux.microsoft.com, alanau@linux.microsoft.com Cc: linux-trace-devel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [RFC PATCH v2 4/7] tracing/user_events: Fixup enable faults asyncly Date: Mon, 14 Nov 2022 16:58:59 -0800 Message-Id: <20221115005902.30458-5-beaub@linux.microsoft.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20221115005902.30458-1-beaub@linux.microsoft.com> References: <20221115005902.30458-1-beaub@linux.microsoft.com> MIME-Version: 1.0 X-Spam-Status: No, score=-19.8 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,ENV_AND_HDR_SPF_MATCH,RCVD_IN_DNSWL_MED, SPF_HELO_PASS,SPF_PASS,USER_IN_DEF_DKIM_WL,USER_IN_DEF_SPF_WL autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1749522120832857896?= X-GMAIL-MSGID: =?utf-8?q?1749522120832857896?= When events are enabled within the various tracing facilities, such as ftrace/perf, the event_mutex is held. As events are enabled pages are accessed. We do not want page faults to occur under this lock. Instead queue the fault to a workqueue to be handled in a process context safe way without the lock. The enable address is marked faulting while the async fault-in occurs. This ensures that we don't attempt to fault-in more than is necessary. Once the page has been faulted in, an address write is re-attempted. If the page couldn't fault-in, then we wait until the next time the event is enabled to prevent any potential infinite loops. Signed-off-by: Beau Belgrave --- kernel/trace/trace_events_user.c | 115 +++++++++++++++++++++++++++++-- 1 file changed, 110 insertions(+), 5 deletions(-) diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c index d5e926fe7dae..569e97f713da 100644 --- a/kernel/trace/trace_events_user.c +++ b/kernel/trace/trace_events_user.c @@ -99,11 +99,25 @@ struct user_event_enabler { /* Bits 0-5 are for the bit to update upon enable/disable (0-63 allowed) */ #define ENABLE_VAL_BIT_MASK 0x3F +/* Bit 6 is for faulting status of enablement */ +#define ENABLE_VAL_FAULTING_BIT 6 + /* Only duplicate the bit value */ #define ENABLE_VAL_DUP_MASK ENABLE_VAL_BIT_MASK #define ENABLE_VALUE_BITS(e) ((e)->values & ENABLE_VAL_BIT_MASK) +#define ENABLE_BITOPS(e) ((unsigned long *)&(e)->values) + +/* Used for asynchronous faulting in of pages */ +struct user_event_enabler_fault { + struct work_struct work; + struct user_event_mm *mm; + struct user_event_enabler *enabler; +}; + +static struct kmem_cache *fault_cache; + /* Global list of memory descriptors using user_events */ static LIST_HEAD(user_event_mms); static DEFINE_SPINLOCK(user_event_mms_lock); @@ -259,7 +273,85 @@ static int user_event_mm_fault_in(struct user_event_mm *mm, unsigned long uaddr) } static int user_event_enabler_write(struct user_event_mm *mm, - struct user_event_enabler *enabler) + struct user_event_enabler *enabler, + bool fixup_fault); + +static void user_event_enabler_fault_fixup(struct work_struct *work) +{ + struct user_event_enabler_fault *fault = container_of( + work, struct user_event_enabler_fault, work); + struct user_event_enabler *enabler = fault->enabler; + struct user_event_mm *mm = fault->mm; + unsigned long uaddr = enabler->addr; + int ret; + + ret = user_event_mm_fault_in(mm, uaddr); + + if (ret) { + struct user_event *user = enabler->event; + + pr_warn("user_events: Fault for mm: 0x%pK @ 0x%llx event: %s\n", + mm->mm, (unsigned long long)uaddr, EVENT_NAME(user)); + } + + /* Prevent state changes from racing */ + mutex_lock(&event_mutex); + + /* + * If we managed to get the page, re-issue the write. We do not + * want to get into a possible infinite loop, which is why we only + * attempt again directly if the page came in. If we couldn't get + * the page here, then we will try again the next time the event is + * enabled/disabled. + */ + clear_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler)); + + if (!ret) { + mmap_read_lock(mm->mm); + user_event_enabler_write(mm, enabler, true); + mmap_read_unlock(mm->mm); + } + + mutex_unlock(&event_mutex); + + /* In all cases we no longer need the mm or fault */ + user_event_mm_put(mm); + kmem_cache_free(fault_cache, fault); +} + +static bool user_event_enabler_queue_fault(struct user_event_mm *mm, + struct user_event_enabler *enabler) +{ + struct user_event_enabler_fault *fault; + + fault = kmem_cache_zalloc(fault_cache, GFP_NOWAIT | __GFP_NOWARN); + + if (!fault) + return false; + + INIT_WORK(&fault->work, user_event_enabler_fault_fixup); + fault->mm = user_event_mm_get(mm); + fault->enabler = enabler; + + /* Don't try to queue in again while we have a pending fault */ + set_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler)); + + if (!schedule_work(&fault->work)) { + /* Allow another attempt later */ + clear_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler)); + + user_event_mm_put(mm); + kmem_cache_free(fault_cache, fault); + + return false; + } + + return true; +} + +static int user_event_enabler_write(struct user_event_mm *mm, + struct user_event_enabler *enabler, + bool fixup_fault) { unsigned long uaddr = enabler->addr; unsigned long *ptr; @@ -270,11 +362,19 @@ static int user_event_enabler_write(struct user_event_mm *mm, lockdep_assert_held(&event_mutex); mmap_assert_locked(mm->mm); + if (unlikely(test_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler)))) + return -EBUSY; + ret = pin_user_pages_remote(mm->mm, uaddr, 1, FOLL_WRITE | FOLL_NOFAULT, &page, NULL, NULL); - if (ret <= 0) { - pr_warn("user_events: Enable write failed\n"); + if (unlikely(ret <= 0)) { + if (!fixup_fault) + return ret; + + if (!user_event_enabler_queue_fault(mm, enabler)) + pr_warn("user_events: Unable to queue fault handler\n"); + return ret; } @@ -306,7 +406,7 @@ static void user_event_enabler_update(struct user_event *user) list_for_each_entry_rcu(enabler, &mm->enablers, link) if (enabler->event == user) - user_event_enabler_write(mm, enabler); + user_event_enabler_write(mm, enabler, true); rcu_read_unlock(); mmap_read_unlock(mm->mm); @@ -539,7 +639,7 @@ static struct user_event_enabler /* Attempt to reflect the current state within the process */ mmap_read_lock(user_mm->mm); - *write_result = user_event_enabler_write(user_mm, enabler); + *write_result = user_event_enabler_write(user_mm, enabler, false); mmap_read_unlock(user_mm->mm); /* @@ -2172,6 +2272,11 @@ static int __init trace_events_user_init(void) { int ret; + fault_cache = KMEM_CACHE(user_event_enabler_fault, 0); + + if (!fault_cache) + return -ENOMEM; + init_group = user_event_group_create(&init_user_ns); if (!init_group)