Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752724AbbGOSD7 (ORCPT ); Wed, 15 Jul 2015 14:03:59 -0400 Received: from mail-yk0-f171.google.com ([209.85.160.171]:34050 "EHLO mail-yk0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751592AbbGOSD6 (ORCPT ); Wed, 15 Jul 2015 14:03:58 -0400 Date: Wed, 15 Jul 2015 14:03:55 -0400 From: Tejun Heo To: Dan Williams Cc: Laurent Pinchart , Linux Kernel Mailing List Subject: Re: Is devm_* broken ? Message-ID: <20150715180355.GH15934@mtj.duckdns.org> References: <1503739.gVWYM3p8QD@avalon> 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: 1648 Lines: 36 Hello, On Wed, Jul 15, 2015 at 10:00:54AM -0700, Dan Williams wrote: > Sounds like a real problem. The drivers I've used devm with have an > upper layer that prevents this crash, but that's not much consolation. > I think adding lifetime to devm allocations would be useful that way > ->probe() and open() can do a devres_get() while ->remove() and > close() can do a devres_put(). Perhaps I'm also missing something > obvious though... Hmmm... so this really is a general lifetime management problem and also why sysfs implements revoke semantics. As memory allocated by devm_kmalloc() isn't tied to any specific hardware, it seems a bit murky here but if you consider any other resources, this is clear - a driver must not access any resources once detach is complete. These aren't resources which can be detached and then held while draining existing userland references. They immediately conflict with the next driver which is gonna attach to the device. A driver should isolate and drain on-going accesses from userland before finishing detaching one way or another. No resources attached to the hardware side can't be held once detaching is complete. If a piece of memory isn't attached to the harware side but the userland interface side which gets isolated and drained after detachment, that shouldn't be allocated via devm - it has "dev" in its name for a reason. Thanks. -- tejun -- 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/