From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bh-25.webhostbox.net ([208.91.199.152]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1ZtHFP-0003Ri-UU for linux-mtd@lists.infradead.org; Mon, 02 Nov 2015 15:42:17 +0000 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 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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