linux-kernel - Re: [PATCH 09/27] mtd: nand: pxa3xx: show device structure in sysfs

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Message-ID: <20140528072513.GA4285@norris-Latitude-E6410>
Date:	Wed, 28 May 2014 00:25:13 -0700
From:	Brian Norris <computersforpeace@...il.com>
To:	Alexander Holler <holler@...oftware.de>
Cc:	Alexander Shiyan <shc_work@...l.ru>,
	David Woodhouse <dwmw2@...radead.org>,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/27] mtd: nand: pxa3xx: show device structure in sysfs

On Tue, May 27, 2014 at 08:01:55AM +0200, Alexander Holler wrote:
> Am 27.05.2014 05:12, schrieb Alexander Shiyan:
> >Should we add "driver.owner = THIS_MODULE" field for struct platform_driver in this case?
> 
> Yes. I assumed all drivers/modules already had an owner. I will
> check them all and will send a v2 for those which don't have one. I
> wonder what this field is used for if it works without. ;)

Looks like the mtd->owner essentially filters down to a try_module_get()
(called in the get_mtd_device() API) which ensures that MTD users (e.g.,
mtdblock, UBI, etc.) hold a refcount on the driver module. If the owner
is not set properly by a driver, then try_module_get() just does a
silent no-op, so the user is none the wiser... until they try to rmmod
their MTD driver while it's being used by UBI/UBIFS!

Regards,
Brian
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