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 X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A784CC5DF62 for ; Wed, 6 Nov 2019 05:17:00 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5011B206A3 for ; Wed, 6 Nov 2019 05:17:00 +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 5011B206A3 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) Received: by kanga.kvack.org (Postfix, from userid 40) id 0F9DA6B0275; Wed, 6 Nov 2019 00:17:00 -0500 (EST) 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-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-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; } _