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

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Date:	Thu, 4 Aug 2016 19:46:33 +0530
From:	Sandeep Jain <Sandeep_Jain@...tor.com>
To:	<dwmw2@...radead.org>, <computersforpeace@...il.com>
CC:	<linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
	Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>,
	Sandeep Jain <Sandeep_Jain@...tor.com>
Subject: [PATCH v1 1/2] mtd: m25p80: lock module while used

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);
-- 
1.7.9.5