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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5CDEAC43334 for ; Tue, 14 Jun 2022 22:04:24 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D17266B0074; Tue, 14 Jun 2022 18:04:21 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C9C5A6B0075; Tue, 14 Jun 2022 18:04:21 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AC7836B0078; Tue, 14 Jun 2022 18:04:21 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 8B55D6B0074 for ; Tue, 14 Jun 2022 18:04:21 -0400 (EDT) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay11.hostedemail.com (Postfix) with ESMTP id 6737680F84 for ; Tue, 14 Jun 2022 22:04:21 +0000 (UTC) X-FDA: 79578220722.19.DD12D85 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf10.hostedemail.com (Postfix) with ESMTP id EFFD1C008C for ; Tue, 14 Jun 2022 22:04:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1655244260; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Dq7PRgfYueFTliKJ1ZMorr4opGVcM+i2DptJCykcaYo=; b=JKHLiqO4Wxr6CYLhwKIXzCWCweqft29Kn9XEpIpBbJay9T/4iDAYO+fcufRGrPR6X1FBrW Lc5+q8iYWdyhv03ACfloWxidpFiAktLam9J5upVV0SUWZbgq3hVgj6ypjBL8QLqXq9zPZT 1WuJiEOZ/hEu5srEgQkrkl3aJKtpoMI= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-357-nbuAHervO9iXkg1fBAknOw-1; Tue, 14 Jun 2022 18:04:15 -0400 X-MC-Unique: nbuAHervO9iXkg1fBAknOw-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id A8AB685A581; Tue, 14 Jun 2022 22:04:14 +0000 (UTC) Received: from llong.com (unknown [10.22.33.116]) by smtp.corp.redhat.com (Postfix) with ESMTP id 66D30492CA2; Tue, 14 Jun 2022 22:04:14 +0000 (UTC) From: Waiman Long To: Catalin Marinas , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Muchun Song , Waiman Long Subject: [PATCH v2 2/3] mm/kmemleak: Skip unlikely objects in kmemleak_scan() without taking lock Date: Tue, 14 Jun 2022 18:03:58 -0400 Message-Id: <20220614220359.59282-3-longman@redhat.com> In-Reply-To: <20220614220359.59282-1-longman@redhat.com> References: <20220614220359.59282-1-longman@redhat.com> MIME-Version: 1.0 Content-type: text/plain Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.85 on 10.11.54.9 ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655244261; a=rsa-sha256; cv=none; b=wFST2fgizlbswErMz2ixXuAl/GZMDAukx+PE3saBfZiG3ktazvrvBf/ykURKqWNAGJvKet aD9Y5E++bt1Yt5YI6heIx79rlNPrfSj9GkBsMmrqBikLvXJI8R6dgBVz1AbEcXRugs9IpV O1omJrpkXiWdSgt0AMRmMl2eHBfHTlo= ARC-Authentication-Results: i=1; imf10.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=JKHLiqO4; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf10.hostedemail.com: domain of longman@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=longman@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1655244261; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Dq7PRgfYueFTliKJ1ZMorr4opGVcM+i2DptJCykcaYo=; b=H9i8nrKzR1jqFbhXxv1yvvqC8FckFBtyxurR+keE/r2AKRWhWQ1KoIR/kC0hQGMLWwCPLH GwOFJ5vltTa14H0o5YS5mFEbc0C7OUVP0EFykjpdbJtkRuHkcQlWRU0uie7eIdGxoEOCB9 LXpaSxESM/Nvj7f9qgtI53RhHyKVG50= X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: EFFD1C008C X-Stat-Signature: jsx9am3gxo1u1x4zbzf3rh7zm9quba1d Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=JKHLiqO4; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf10.hostedemail.com: domain of longman@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=longman@redhat.com X-Rspam-User: X-HE-Tag: 1655244260-186745 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: There are 3 RCU-based object iteration loops in kmemleak_scan(). Because of the need to take RCU read lock, we can't insert cond_resched() into the loop like other parts of the function. As there can be millions of objects to be scanned, it takes a while to iterate all of them. The kmemleak functionality is usually enabled in a debug kernel which is much slower than a non-debug kernel. With sufficient number of kmemleak objects, the time to iterate them all may exceed 22s causing soft lockup. watchdog: BUG: soft lockup - CPU#3 stuck for 22s! [kmemleak:625] In this particular bug report, the soft lockup happen in the 2nd iteration loop. In the 2nd and 3rd loops, most of the objects are checked and then skipped under the object lock. Only a selected fews are modified. Those objects certainly need lock protection. However, the lock/unlock operation is slow especially with interrupt disabling and enabling included. We can actually do some basic check like color_white() without taking the lock and skip the object accordingly. Of course, this kind of check is racy and may miss objects that are being modified concurrently. The cost of missed objects, however, is just that they will be discovered in the next scan instead. The advantage of doing so is that iteration can be done much faster especially with LOCKDEP enabled in a debug kernel. With a debug kernel running on a 2-socket 96-thread x86-64 system (HZ=1000), the 2nd and 3rd iteration loops speedup with this patch on the first kmemleak_scan() call after bootup is shown in the table below. Before patch After patch Loop # # of objects Elapsed time # of objects Elapsed time ------ ------------ ------------ ------------ ------------ 2 2,599,850 2.392s 2,596,364 0.266s 3 2,600,176 2.171s 2,597,061 0.260s This patch reduces loop iteration times by about 88%. This will greatly reduce the chance of a soft lockup happening in the 2nd or 3rd iteration loops. Even though the first loop runs a little bit faster, it can still be problematic if many kmemleak objects are there. As the object count has to be modified in every object, we cannot avoid taking the object lock. So other way to prevent soft lockup will be needed. Signed-off-by: Waiman Long Reviewed-by: Catalin Marinas --- mm/kmemleak.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/mm/kmemleak.c b/mm/kmemleak.c index dad9219c972c..7dd64139a7c7 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -1508,6 +1508,13 @@ static void kmemleak_scan(void) */ rcu_read_lock(); list_for_each_entry_rcu(object, &object_list, object_list) { + /* + * This is racy but we can save the overhead of lock/unlock + * calls. The missed objects, if any, should be caught in + * the next scan. + */ + if (!color_white(object)) + continue; raw_spin_lock_irq(&object->lock); if (color_white(object) && (object->flags & OBJECT_ALLOCATED) && update_checksum(object) && get_object(object)) { @@ -1535,6 +1542,13 @@ static void kmemleak_scan(void) */ rcu_read_lock(); list_for_each_entry_rcu(object, &object_list, object_list) { + /* + * This is racy but we can save the overhead of lock/unlock + * calls. The missed objects, if any, should be caught in + * the next scan. + */ + if (!color_white(object)) + continue; raw_spin_lock_irq(&object->lock); if (unreferenced_object(object) && !(object->flags & OBJECT_REPORTED)) { -- 2.31.1