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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4444EC4167B for ; Fri, 16 Dec 2022 03:41:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229736AbiLPDlT (ORCPT ); Thu, 15 Dec 2022 22:41:19 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56820 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229453AbiLPDlR (ORCPT ); Thu, 15 Dec 2022 22:41:17 -0500 Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [IPv6:2a03:a000:7:0:5054:ff:fe1c:15ff]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 39C454045A; Thu, 15 Dec 2022 19:41:12 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=uFjXacM4V95MITfaVTbj36apFcWXHC9KNgQ5sG+WTEI=; b=G0kCpgSZN1EUotUaOgsFdEeJKi nvprcIE7kGY++o1ePwPpDikIET9h5IfUZv5fKlyM9T+MTa1WtL7BcWlQIPJ1qncj5D+3zA5RSHenM uuyFF3ICu5NIzeaP0IqVitYV1v16gVRNvoLEa0jQfnaD1i0TEBXhJgRZw8l1Ci4W394x7vfLSaZh+ 6/Krg8qkikKZ4XSbLyCPUHUEHNUNIbxFpj60CINFzQvZ9z22cE+LhEfajKhJruE+eTK0LWmHdw57d AKjOOLtlDJvasjaHWIMZUF9PavT5KPIWZU8a2Isujw/v7ohpSBnpKB9dreiKRAvkb6tt6IQnpuBrH j2FDVTNw==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.96 #2 (Red Hat Linux)) id 1p61at-00CAKK-2V; Fri, 16 Dec 2022 03:41:07 +0000 Date: Fri, 16 Dec 2022 03:41:07 +0000 From: Al Viro To: Damien Le Moal Cc: Wei Chen , linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, syzbot , linux-fsdevel , Chuck Lever , Jeff Layton , Peter Zijlstra , Linus Torvalds Subject: Re: possible deadlock in __ata_sff_interrupt Message-ID: References: <5eff70b8-04fc-ee87-973a-2099a65f6e29@opensource.wdc.com> <80dc24c5-2c4c-b8da-5017-31aae65a4dfa@opensource.wdc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <80dc24c5-2c4c-b8da-5017-31aae65a4dfa@opensource.wdc.com> Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 16, 2022 at 10:44:06AM +0900, Damien Le Moal wrote: > The original & complete lockdep splat is in the report email here: > > https://marc.info/?l=linux-ide&m=167094379710177&w=2 > > It looks like a spinlock is taken for the fasync stuff without irq > disabled and that same spinlock is needed in kill_fasync() which is > itself called (potentially) with IRQ disabled. Hence the splat. In any > case, that is how I understand the issue. But as mentioned above, given > that I can see many drivers calling kill_fasync() with irq disabled, I > wonder if this is a genuine potential problem or a false negative. OK, I'm about to fall asleep, so I might very well be missing something obvious, but... CPU1: ptrace(2) ptrace_check_attach() read_lock(&tasklist_lock); CPU2: setpgid(2) write_lock_irq(&tasklist_lock); spins CPU1: takes an interrupt that would call kill_fasync(). grep and the first instance of kill_fasync() is in hpet_interrupt() - it's not something exotic. IRQs disabled on CPU2 won't stop it. kill_fasync(..., SIGIO, ...) kill_fasync_rcu() read_lock_irqsave(&fa->fa_lock, flags); send_sigio() read_lock_irqsave(&fown->lock, flags); read_lock(&tasklist_lock); ... and CPU1 spins as well. It's not a matter of kill_fasync() called with IRQs disabled; the problem is kill_fasync() called from interrupt taken while holding tasklist_lock at least shared. Somebody trying to grab it on another CPU exclusive before we get to send_sigio() from kill_fasync() will end up spinning and will make us spin as well. I really hope that's just me not seeing something obvious - we had kill_fasync() called in IRQ handlers since way back and we had tasklist_lock taken shared without disabling IRQs for just as long.