linux-kernel - Re: [PATCH v1 1/2] mtd: m25p80: lock module while used

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Date:   Sat, 5 Nov 2016 08:24:24 +0100
From:   Marek Vasut <marek.vasut@...il.com>
To:     Sandeep Jain <Sandeep_Jain@...tor.com>, dwmw2@...radead.org,
        computersforpeace@...il.com
Cc:     linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
Subject: Re: [PATCH v1 1/2] mtd: m25p80: lock module while used

On 11/03/2016 12:39 PM, Sandeep Jain wrote:
> Dear Maintainers,
> 	Requesting for your attention for patch review/merge.
> 
> Thanks & Regards,
> Sandeep Jain
> 
> On Thu, Aug 04, 2016 at 07:46:33PM +0530, Sandeep Jain wrote:
>> From: Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
>>
>> The change controls module users counter, which prevents to get
>> accidental oops on module unload while it is in use by mtd subsystem:
>>
>> % dd if=/dev/mtd0 of=/dev/null &
>> % rmmod m25p80
>>
>> Removing MTD device #0 (spi32766.0) with use count 1
>> Unable to handle kernel paging request at virtual address 7f4fb7f8
>> pgd = bd094000
>> [7f4fb7f8] *pgd=4cb66811, *pte=00000000, *ppte=00000000
>> Internal error: Oops: 80000007 [#1] PREEMPT SMP ARM
>>
>> Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
>> Signed-off-by: Sandeep Jain <Sandeep_Jain@...tor.com>
>> ---
>>  drivers/mtd/devices/m25p80.c |   15 +++++++++++++++
>>  1 file changed, 15 insertions(+)
>>
>> diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
>> index 9cf7fcd..2eb1530 100644
>> --- a/drivers/mtd/devices/m25p80.c
>> +++ b/drivers/mtd/devices/m25p80.c
>> @@ -185,6 +185,19 @@ static ssize_t m25p80_read(struct spi_nor *nor, loff_t from, size_t len,
>>  	return ret;
>>  }
>>  
>> +static void m25p80_put(struct mtd_info *mtd)
>> +{
>> +	module_put(THIS_MODULE);
>> +}
>> +
>> +static int m25p80_get(struct mtd_info *mtd)
>> +{
>> +	if (!try_module_get(THIS_MODULE))
>> +		return -ENODEV;
>> +
>> +	return 0;
>> +}
>> +
>>  /*
>>   * board specific setup should have ensured the SPI clock used here
>>   * matches what the READ command supports, at least until this driver
>> @@ -212,6 +225,8 @@ static int m25p_probe(struct spi_device *spi)
>>  	nor->write = m25p80_write;
>>  	nor->write_reg = m25p80_write_reg;
>>  	nor->read_reg = m25p80_read_reg;
>> +	nor->mtd._put_device = m25p80_put;
>> +	nor->mtd._get_device = m25p80_get;
>>  
>>  	nor->dev = &spi->dev;
>>  	spi_nor_set_flash_node(nor, spi->dev.of_node);

This makes me ponder how many other drivers suffer from this issue and
whether you shouldn't fix this in the core code instead. What do you think?

-- 
Best regards,
Marek Vasut