From patchwork Sat Feb 26 01:29:39 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 546420 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 CCBCEC433F5 for ; Sat, 26 Feb 2022 01:29:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230104AbiBZBaU (ORCPT ); Fri, 25 Feb 2022 20:30:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48422 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229536AbiBZBaQ (ORCPT ); Fri, 25 Feb 2022 20:30:16 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D2C141DB3E8; Fri, 25 Feb 2022 17:29:42 -0800 (PST) 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 7C874B833C4; Sat, 26 Feb 2022 01:29:41 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 147F8C340E7; Sat, 26 Feb 2022 01:29:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1645838980; bh=6zoPMjPhk8gkXk/MAKx8H4tUlW/Qvc5x7PmQA3QWYFo=; h=Date:To:From:Subject:From; b=rnTw/LyRLNAAtoSrGrXvMD3vxA1A8JGK58VXE5yuJsxyQd5zxSKPQ8bTMbo8H/H7N u6IbEZBoMzaCIbayRZE1Vf7rI/ERYyC9eXsIlh100eCgaJNfeMe9GQgTTHwcOfUtvi pi+Rxrp0Nyh3ZwnnY2T0ejulJ1wPV2MzJtPB9XwU= Date: Fri, 25 Feb 2022 17:29:39 -0800 To: mm-commits@vger.kernel.org, zealci@zte.com.cn, yang.yang29@zte.com.cn, stable@vger.kernel.org, rogerq@kernel.org, ran.xiaokai@zte.com.cn, naoya.horiguchi@nec.com, minchan@kernel.org, mhocko@kernel.org, jiang.xuexin@zte.com.cn, hughd@google.com, hannes@cmpxchg.org, guo.ziliang@zte.com.cn, akpm@linux-foundation.org From: Andrew Morton Subject: + mm-swap-get-rid-of-deadloop-in-swapin-readahead.patch added to -mm tree Message-Id: <20220226012940.147F8C340E7@smtp.kernel.org> Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org The patch titled Subject: mm: swap: get rid of deadloop in swapin readahead has been added to the -mm tree. Its filename is mm-swap-get-rid-of-deadloop-in-swapin-readahead.patch This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/mm-swap-get-rid-of-deadloop-in-swapin-readahead.patch and later at https://ozlabs.org/~akpm/mmotm/broken-out/mm-swap-get-rid-of-deadloop-in-swapin-readahead.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Guo Ziliang Subject: mm: swap: get rid of deadloop in swapin readahead In our testing, a deadloop task was found. Through sysrq printing, same stack was found every time, as follows: __swap_duplicate+0x58/0x1a0 swapcache_prepare+0x24/0x30 __read_swap_cache_async+0xac/0x220 read_swap_cache_async+0x58/0xa0 swapin_readahead+0x24c/0x628 do_swap_page+0x374/0x8a0 __handle_mm_fault+0x598/0xd60 handle_mm_fault+0x114/0x200 do_page_fault+0x148/0x4d0 do_translation_fault+0xb0/0xd4 do_mem_abort+0x50/0xb0 The reason for the deadloop is that swapcache_prepare() always returns EEXIST, indicating that SWAP_HAS_CACHE has not been cleared, so that it cannot jump out of the loop. We suspect that the task that clears the SWAP_HAS_CACHE flag never gets a chance to run. We try to lower the priority of the task stuck in a deadloop so that the task that clears the SWAP_HAS_CACHE flag will run. The results show that the system returns to normal after the priority is lowered. In our testing, multiple real-time tasks are bound to the same core, and the task in the deadloop is the highest priority task of the core, so the deadloop task cannot be preempted. Although cond_resched() is used by __read_swap_cache_async, it is an empty function in the preemptive system and cannot achieve the purpose of releasing the CPU. A high-priority task cannot release the CPU unless preempted by a higher-priority task. But when this task is already the highest priority task on this core, other tasks will not be able to be scheduled. So we think we should replace cond_resched() with schedule_timeout_uninterruptible(1), schedule_timeout_interruptible will call set_current_state first to set the task state, so the task will be removed from the running queue, so as to achieve the purpose of giving up the CPU and prevent it from running in kernel mode for too long. (akpm: ugly hack becomes uglier. But it fixes the issue in a backportable-to-stable fashion while we hopefully work on something better) Link: https://lkml.kernel.org/r/20220221111749.1928222-1-cgel.zte@gmail.com Signed-off-by: Guo Ziliang Reported-by: Zeal Robot Reviewed-by: Ran Xiaokai Reviewed-by: Jiang Xuexin Reviewed-by: Yang Yang Cc: Naoya Horiguchi Cc: Michal Hocko Cc: Minchan Kim Cc: Johannes Weiner Cc: Roger Quadros Cc: Ziliang Guo Cc: Hugh Dickins Cc: Signed-off-by: Andrew Morton --- mm/swap_state.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/swap_state.c~mm-swap-get-rid-of-deadloop-in-swapin-readahead +++ a/mm/swap_state.c @@ -478,7 +478,7 @@ struct page *__read_swap_cache_async(swp * __read_swap_cache_async(), which has set SWAP_HAS_CACHE * in swap_map, but not yet added its page to swap cache. */ - cond_resched(); + schedule_timeout_uninterruptible(1); } /*