Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752143AbbBSCZW (ORCPT ); Wed, 18 Feb 2015 21:25:22 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:49617 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751456AbbBSCZU (ORCPT ); Wed, 18 Feb 2015 21:25:20 -0500 Date: Wed, 18 Feb 2015 18:25:19 -0800 From: greg KH To: Lucas De Marchi Cc: Rusty Russell , Harish Jenny K N , linux-modules , lkml Subject: Re: [PATCH] libkmod-module: Remove directory existence check for KMOD_MODULE_BUILTIN Message-ID: <20150219022519.GD8089@kroah.com> References: <1424177796-17923-1-git-send-email-harish_kandiga@mentor.com> <874mqjuaky.fsf@rustcorp.com.au> <87vbiysv1v.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2341 Lines: 54 On Wed, Feb 18, 2015 at 11:19:14PM -0200, Lucas De Marchi wrote: > On Wed, Feb 18, 2015 at 8:40 PM, Rusty Russell wrote: > > Lucas De Marchi writes: > >> On Wed, Feb 18, 2015 at 2:07 AM, Rusty Russell wrote: > >> Yeah, I just thought (an wanted that) the attributes were being > >> created first and then hooked up in the sysfs tree under > >> /sys/module/. I.e. if the directory exists and there's no > >> initstate this is because it's a builtin module. I don't want to > >> wait/sleep on the file to appear because users of > >> kmod_module_get_initstate() may not tolerate this behavior. > >> > >> Looking up at the old module-init-tools, it used an ugly loop with > >> usleep() before trying to read the file again :-/ > >> > >> Can we change kernel side guaranteeing the initstate file appears > >> together with the directory? > > > > Greg? The core problem is that kmod looks for > > /sys/module//initstate; if it's not there, it assumes a builtin > > module. > > Just to make it clear: > > We try to open /sys/module//initstate. If it fails we stat > /sys/module/ checking if it exists and is a directory. If it > does then we assume the module is builtin. > > > However, this is racy when a module is being inserted. Is there a way > > to create this sysfs file and dir atomically? > > Greg, the question is still valid since it'd be nice to have this > guarantee and be able to correctly reply the state with whatever is in > initstate file, but... You should always wait until you get the uevent that the object was added before poking around in sysfs. The kernel will guarantee all of the needed files / directories will be created before that event is sent out. That's why we added the uevent message. So by just busy-spinning on the directory and ignoring the uevent, you are just blindly guessing as to when things are finished, which is racy as you see. So please just wait for the event, then you should be fine, that's what it is there for. thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/