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=-6.8 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,USER_AGENT_GIT autolearn=unavailable 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 26512C17445 for ; Mon, 11 Nov 2019 18:41:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EEAA4214E0 for ; Mon, 11 Nov 2019 18:41:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573497679; bh=2Z0kF615/8pP7GAFhU4mwiF3q5g8Einkwiw0LYuwll8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=T3Q/DBRn/qYpqVzqfUweBrteQVYnBeUQ49rjsZ2RkoOOZZzATIQtl9Ws7N5CQhJC5 f1Dinwr2gXVcBiVx/zS+jpFx6HdByquj6v15MVOpeawoSU8oPCrW0qzW2UbfCZeDHf nLvUC1rSPDFRTGf/YZIdN1TZ0KZlWm+ZRPPLfc10= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729359AbfKKSlN (ORCPT ); Mon, 11 Nov 2019 13:41:13 -0500 Received: from mail.kernel.org ([198.145.29.99]:60468 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729358AbfKKSlN (ORCPT ); Mon, 11 Nov 2019 13:41:13 -0500 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 2D24D21E6F; Mon, 11 Nov 2019 18:41:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573497672; bh=2Z0kF615/8pP7GAFhU4mwiF3q5g8Einkwiw0LYuwll8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=rwF2SMVwLVCh2MC8e4Vljuam5D9rrjW2WFPfnttWoGmKaqFv3j6S5wZdpYXzVXRc1 rmWxFSY2TGg7ZCYaM9Qicb86wEbTv9yMWLbn8zv4Qry5pVK3GnK6EaBAWDdT+7NokE Quv3Kf96TGFM6dQs1wy81FfTsPnzsXoRe4mjLe+c= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Kevin Hao , Linus Torvalds , Andrew Morton Subject: [PATCH 4.19 023/125] dump_stack: avoid the livelock of the dump_lock Date: Mon, 11 Nov 2019 19:27:42 +0100 Message-Id: <20191111181443.570829224@linuxfoundation.org> X-Mailer: git-send-email 2.24.0 In-Reply-To: <20191111181438.945353076@linuxfoundation.org> References: <20191111181438.945353076@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Kevin Hao commit 5cbf2fff3bba8d3c6a4d47c1754de1cf57e2b01f upstream. 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 Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- lib/dump_stack.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) --- a/lib/dump_stack.c +++ b/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; }