From patchwork Wed Nov 6 05:16:57 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 11229317 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 87F1015AB for ; Wed, 6 Nov 2019 05:17:01 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 495E2206A3 for ; Wed, 6 Nov 2019 05:17:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="qFyuIoms" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 495E2206A3 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 1492B6B0274; Wed, 6 Nov 2019 00:17:00 -0500 (EST) Delivered-To: linux-mm-outgoing@kvack.org Received: by kanga.kvack.org (Postfix, from userid 40) id 0F9DA6B0275; Wed, 6 Nov 2019 00:17:00 -0500 (EST) X-Original-To: int-list-linux-mm@kvack.org X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0105C6B0276; Wed, 6 Nov 2019 00:16:59 -0500 (EST) X-Original-To: linux-mm@kvack.org X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0008.hostedemail.com [216.40.44.8]) by kanga.kvack.org (Postfix) with ESMTP id E0D3D6B0274 for ; Wed, 6 Nov 2019 00:16:59 -0500 (EST) Received: from smtpin19.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with SMTP id 5F7928249980 for ; Wed, 6 Nov 2019 05:16:59 +0000 (UTC) X-FDA: 76124693358.19.light51_3cfc575666358 X-Spam-Summary: 2,0,0,cdaaa0825d87fbcc,d41d8cd98f00b204,akpm@linux-foundation.org,:akpm@linux-foundation.org:haokexin@gmail.com::mm-commits@vger.kernel.org:stable@vger.kernel.org:torvalds@linux-foundation.org,RULES_HIT:41:355:379:800:960:967:973:988:989:1260:1263:1345:1381:1431:1437:1534:1541:1711:1730:1747:1777:1792:2198:2199:2393:2525:2559:2563:2682:2685:2693:2731:2859:2902:2933:2937:2939:2942:2945:2947:2951:2954:3022:3138:3139:3140:3141:3142:3352:3865:3866:3867:3870:3934:3936:3938:3941:3944:3947:3950:3953:3956:3959:4321:5007:6261:6653:7514:7576:8599:9025:9545:10004:10913:11026:11658:11914:12043:12048:12296:12297:12517:12519:12555:12679:12783:12986:13069:13311:13357:13846:14181:14384:14721:14849:21080:21324:21451:21627:21939:30012:30054,0,RBL:error,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fp,MSBL:0,DNSBL:neutral,Custom_rules:0:0:0,LFtime:24,LUA_SUMMARY:none X-HE-Tag: light51_3cfc575666358 X-Filterd-Recvd-Size: 2766 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf06.hostedemail.com (Postfix) with ESMTP for ; Wed, 6 Nov 2019 05:16:58 +0000 (UTC) Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id CEB86206A3; Wed, 6 Nov 2019 05:16:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573017418; bh=6SoXQmpFL1pLJ30tuGrZg1GHHjTEWHo92t9q3pvJXso=; h=Date:From:To:Subject:From; b=qFyuIomsckNtmr2V/sFtUsF2WgW8/6DJAnwvA7qMTvar9GKsrLHaXBo1ifEDMnYWa CB16Y8WUsxV3shC3g0JDuhy5ZXb+tA7EmZ/CJvJ/u8Fu9fRzpnq47CZ/ZLJ0KwJPej gmD8/cjcCyY3uZjHAJ3z8jvCbMlemBbM/rlPEL1I= Date: Tue, 05 Nov 2019 21:16:57 -0800 From: akpm@linux-foundation.org To: akpm@linux-foundation.org, haokexin@gmail.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, stable@vger.kernel.org, torvalds@linux-foundation.org Subject: [patch 12/17] dump_stack: avoid the livelock of the dump_lock Message-ID: <20191106051657.fRGxFzH1B%akpm@linux-foundation.org> User-Agent: s-nail v14.8.16 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: From: Kevin Hao Subject: dump_stack: avoid the livelock of the dump_lock In the current code, we use the atomic_cmpxchg() to serialize the output of the dump_stack(), but this implementation suffers the thundering herd problem. We have observed such kind of livelock on a Marvell cn96xx board(24 cpus) when heavily using the dump_stack() in a kprobe handler. Actually we can let the competitors to wait for the releasing of the lock before jumping to atomic_cmpxchg(). This will definitely mitigate the thundering herd problem. Thanks Linus for the suggestion. [akpm@linux-foundation.org: fix comment] Link: http://lkml.kernel.org/r/20191030031637.6025-1-haokexin@gmail.com Fixes: b58d977432c8 ("dump_stack: serialize the output from dump_stack()") Signed-off-by: Kevin Hao Suggested-by: Linus Torvalds Cc: Signed-off-by: Andrew Morton --- lib/dump_stack.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) --- a/lib/dump_stack.c~dump_stack-avoid-the-livelock-of-the-dump_lock +++ a/lib/dump_stack.c @@ -106,7 +106,12 @@ retry: was_locked = 1; } else { local_irq_restore(flags); - cpu_relax(); + /* + * Wait for the lock to release before jumping to + * atomic_cmpxchg() in order to mitigate the thundering herd + * problem. + */ + do { cpu_relax(); } while (atomic_read(&dump_lock) != -1); goto retry; }