Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754143AbbKBPl4 (ORCPT ); Mon, 2 Nov 2015 10:41:56 -0500 Received: from bh-25.webhostbox.net ([208.91.199.152]:49010 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753471AbbKBPlw (ORCPT ); Mon, 2 Nov 2015 10:41:52 -0500 To: Brian Norris Cc: Richard Weinberger , "linux-mtd@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Jesper Nilsson , linux-cris-kernel@axis.com From: Guenter Roeck Subject: Problems with 'mtd: warn when registering the same master many times' Message-ID: <5637843C.10307@roeck-us.net> Date: Mon, 2 Nov 2015 07:41:48 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated_sender: linux@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: authenticated_id: linux@roeck-us.net X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2864 Lines: 57 Brian, I see the following warnings in recent mips qemu tests on linux-next. WARNING: CPU: 0 PID: 1 at drivers/mtd/mtdcore.c:619 mtd_device_parse_register+0x160/0x16c() MTD already registered Looking into the code, this is the result of your patch 'mtd: warn when registering the same master many times'. This patch is supposed to warn if mtd_device_parse_register is called multiple times with the same mtd_info structure pointer as parameter. At the surface, the check appears to make sense. However, it has a problem. The output of "git grep reboot_notifier.notifier_call" in drivers/mtd results in chips/cfi_cmdset_0001.c: mtd->reboot_notifier.notifier_call = cfi_intelext_reboot; chips/cfi_cmdset_0002.c: mtd->reboot_notifier.notifier_call = cfi_amdstd_reboot; mtdcore.c: WARN_ONCE(mtd->reboot_notifier.notifier_call, "MTD already registered\n"); mtdcore.c: if (mtd->_reboot && !mtd->reboot_notifier.notifier_call) { mtdcore.c: mtd->reboot_notifier.notifier_call = mtd_reboot_notifier; As it turns out, the observed warning is not seen because mtd_device_parse_register() is called multiple times. It is seen because mtd->reboot_notifier.notifier_call is already set to cfi_intelext_reboot by the time it is checked. I don't know if this is a bug in the mtd code, or if this is a valid use case. Whatever it is, the warning does not warn about the driver, it warns about a potential inconsistency in the mtd code itself (and if it is is a valid use case, the warning is inappropriate). Maybe it would make sense to change the warning as follows ? WARN_ONCE(mtd->_reboot && mtd->reboot_notifier.notifier_call, "MTD already registered\n"); I am not sure, though, if that is correct, since even that might be a valid use case (a caller registering a cfi based mtd device with a _reboot callback). I also see the warning in crisv32 runtime tests. This is because the code in arch/cris/arch-v32/drivers/axisflashmap.c calls mtd_device_register() multiple times with the same mtd_info argument, each time to register a different partition. I am not sure if the check is appropriate for this case either, since the code calls mtd_device_register(), both 'type' and 'parser_data' are NULL, parse_mtd_partitions() does not do anything, and the problem you are concerned about does not apply. How about changing the warning to something like the following ? WARN_ONCE(types && mtd->_reboot && mtd->reboot_notifier.notifier_call, "MTD already registered\n"); This would eliminate (what I think are) false positives and only warn if there is a real problem. Thanks, Guenter -- 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/