From nobody Sun Oct 19 06:04:47 2025 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 B811AC433FE for ; Wed, 19 Oct 2022 10:58:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233588AbiJSK6X (ORCPT ); Wed, 19 Oct 2022 06:58:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49802 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234687AbiJSK5I (ORCPT ); Wed, 19 Oct 2022 06:57:08 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C0629108DF7; Wed, 19 Oct 2022 03:27:43 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 1CB47B8249C; Wed, 19 Oct 2022 09:07:41 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6424EC433D6; Wed, 19 Oct 2022 09:07:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666170459; bh=LOQm+b4gdhndYidtU+rnK72Qvs2MOTXXFuDNLCJmht0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=mC6FrnnqJZQbP8ggrxdb+cHvWHIpdq8HJTiRKQQUk4im/IoC8XWRWc+xr5jf2Vnht 8ca4zDtR9rsoYIx2Dj/obDDvf1L0NKMZHOrv7+//OemqcRI4Je+5thoZrn+mHfrLIX 2CoEv8oZHGFaZ5VmMyUVJq77OKRMxmQstalTvk6E= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Uladzislau Rezki (Sony)" , "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , Michal Hocko , Sasha Levin Subject: [PATCH 6.0 663/862] rcu: Back off upon fill_page_cache_func() allocation failure Date: Wed, 19 Oct 2022 10:32:30 +0200 Message-Id: <20221019083319.261237319@linuxfoundation.org> X-Mailer: git-send-email 2.38.0 In-Reply-To: <20221019083249.951566199@linuxfoundation.org> References: <20221019083249.951566199@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Michal Hocko [ Upstream commit 093590c16b447f53e66771c8579ae66c96f6ef61 ] The fill_page_cache_func() function allocates couple of pages to store kvfree_rcu_bulk_data structures. This is a lightweight (GFP_NORETRY) allocation which can fail under memory pressure. The function will, however keep retrying even when the previous attempt has failed. This retrying is in theory correct, but in practice the allocation is invoked from workqueue context, which means that if the memory reclaim gets stuck, these retries can hog the worker for quite some time. Although the workqueues subsystem automatically adjusts concurrency, such adjustment is not guaranteed to happen until the worker context sleeps. And the fill_page_cache_func() function's retry loop is not guaranteed to sleep (see the should_reclaim_retry() function). And we have seen this function cause workqueue lockups: kernel: BUG: workqueue lockup - pool cpus=3D93 node=3D1 flags=3D0x1 nice=3D= 0 stuck for 32s! [...] kernel: pool 74: cpus=3D37 node=3D0 flags=3D0x1 nice=3D0 hung=3D32s workers= =3D2 manager: 2146 kernel: pwq 498: cpus=3D249 node=3D1 flags=3D0x1 nice=3D0 active=3D4/256 = refcnt=3D5 kernel: in-flight: 1917:fill_page_cache_func kernel: pending: dbs_work_handler, free_work, kfree_rcu_monitor Originally, we thought that the root cause of this lockup was several retries with direct reclaim, but this is not yet confirmed. Furthermore, we have seen similar lockups without any heavy memory pressure. This suggests that there are other factors contributing to these lockups. However, it is not really clear that endless retries are desireable. So let's make the fill_page_cache_func() function back off after allocation failure. Cc: Uladzislau Rezki (Sony) Cc: "Paul E. McKenney" Cc: Frederic Weisbecker Cc: Neeraj Upadhyay Cc: Josh Triplett Cc: Steven Rostedt Cc: Mathieu Desnoyers Cc: Lai Jiangshan Cc: Joel Fernandes Signed-off-by: Michal Hocko Reviewed-by: Uladzislau Rezki (Sony) Signed-off-by: Paul E. McKenney Signed-off-by: Sasha Levin --- kernel/rcu/tree.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 79aea7df4345..eb435941e92f 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3183,15 +3183,16 @@ static void fill_page_cache_func(struct work_struct= *work) bnode =3D (struct kvfree_rcu_bulk_data *) __get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_N= OWARN); =20 - if (bnode) { - raw_spin_lock_irqsave(&krcp->lock, flags); - pushed =3D put_cached_bnode(krcp, bnode); - raw_spin_unlock_irqrestore(&krcp->lock, flags); + if (!bnode) + break; =20 - if (!pushed) { - free_page((unsigned long) bnode); - break; - } + raw_spin_lock_irqsave(&krcp->lock, flags); + pushed =3D put_cached_bnode(krcp, bnode); + raw_spin_unlock_irqrestore(&krcp->lock, flags); + + if (!pushed) { + free_page((unsigned long) bnode); + break; } } =20 --=20 2.35.1