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 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 10B5CC433E0 for ; Sun, 24 May 2020 11:42:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E21DB20823 for ; Sun, 24 May 2020 11:42:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590320548; bh=Hsa4osmGTB+icwS6CCShOt0I44y6x7wldglePjcjJcU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=F9YLAPLt5B7FKaXlEz/rkHexBglCqeU0W2DP9pF6KqpkDzSdNDJWpvycpvz6MOGr+ EL7X8dEDpFce85bTfZhLxkH/4rW+1HMbkTGsS+kiOtvYzuGfupA+5rMJcpPpsDZ0on A3X5mmbSu6AwJoyZ2Ci1FUX7rKQsKZG4FRJisuX8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729387AbgEXLm2 (ORCPT ); Sun, 24 May 2020 07:42:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:54298 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727101AbgEXLm1 (ORCPT ); Sun, 24 May 2020 07:42:27 -0400 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 77EC42075F; Sun, 24 May 2020 11:42:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590320546; bh=Hsa4osmGTB+icwS6CCShOt0I44y6x7wldglePjcjJcU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=O6CotyABalJCSDuHY3tmlvjSdcdWp6zEG42vxCz6vzLMaQvVCPPkP07oo1RMKcnT7 W+/p0GUomGACS7aFMGo2SWuZLy1yJfScXh1uaRDL3HWDqB0whvkBiNcNVKE4mK2aVj rLTkcwH06eeRmHlwkqhCufFoYPgiYMII/KRPA8ME= Date: Sun, 24 May 2020 13:42:23 +0200 From: Greg Kroah-Hartman To: Dmitry Torokhov Cc: Randy Dunlap , Heikki Krogerus , lkml , Naresh Kamboju , kernel test robot , Brendan Higgins , "Rafael J. Wysocki" Subject: Re: [PATCH] kobject: Make sure the parent does not get released before its children Message-ID: <20200524114223.GA1942568@kroah.com> References: <20200513151840.36400-1-heikki.krogerus@linux.intel.com> <20200523153643.GA226270@kroah.com> <7a5e4740-8099-ef70-776f-0d92ce84ab3d@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, May 23, 2020 at 12:04:30PM -0700, Dmitry Torokhov wrote: > On Sat, May 23, 2020 at 8:48 AM Randy Dunlap wrote: > > > > On 5/23/20 8:36 AM, Greg Kroah-Hartman wrote: > > > On Wed, May 13, 2020 at 06:18:40PM +0300, Heikki Krogerus wrote: > > >> In the function kobject_cleanup(), kobject_del(kobj) is > > >> called before the kobj->release(). That makes it possible to > > >> release the parent of the kobject before the kobject itself. > > >> > > >> To fix that, adding function __kboject_del() that does > > >> everything that kobject_del() does except release the parent > > >> reference. kobject_cleanup() then calls __kobject_del() > > >> instead of kobject_del(), and separately decrements the > > >> reference count of the parent kobject after kobj->release() > > >> has been called. > > >> > > >> Reported-by: Naresh Kamboju > > >> Reported-by: kernel test robot > > >> Fixes: 7589238a8cf3 ("Revert "software node: Simplify software_node_release() function"") > > >> Suggested-by: "Rafael J. Wysocki" > > >> Signed-off-by: Heikki Krogerus > > >> Reviewed-by: Rafael J. Wysocki > > >> Reviewed-by: Brendan Higgins > > >> Tested-by: Brendan Higgins > > >> Acked-by: Randy Dunlap > > >> --- > > >> lib/kobject.c | 30 ++++++++++++++++++++---------- > > >> 1 file changed, 20 insertions(+), 10 deletions(-) > > > > > > Stepping back, now that it turns out this patch causes more problems > > > than it fixes, how is everyone reproducing the original crash here? > > > > Just load lib/test_printf.ko and boom! > > > > > > > Is it just the KUNIT_DRIVER_PE_TEST that is causing the issue? > > > > > > In looking at 7589238a8cf3 ("Revert "software node: Simplify > > > software_node_release() function""), the log messages there look > > > correct. sysfs can't create a duplicate file, and so when your test is > > > written to try to create software nodes, you always have to check the > > > return value. If you run the test in parallel, or before another test > > > has had a chance to clean up, the function will fail, correctly. > > > > > > So what real-world thing is this test "failure" trying to show? > > Well, not sure about the test, but speaking more generally, should not > we postpone releasing parent's reference until we are in > kobj->release() handler? I.e. after all child state is cleared, and > all memory is freed, _then_ we unpin the parent? That's what the patch was trying to do in a way. But I think you are right, we should _only_ be doing it at that point in time, and no other, which the patch was not doing. Let me go try that and see what happens... thanks, greg k-h