linux-kernel - [PATCH 1/2] brd: Fix the partitions BUG

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Message-ID: <53D8FE1F.1060009@plexistor.com>
Date:	Wed, 30 Jul 2014 17:15:59 +0300
From:	Boaz Harrosh <boaz@...xistor.com>
To:	Jens Axboe <axboe@...nel.dk>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Matthew Wilcox <willy@...ux.intel.com>
CC:	linux-scsi <linux-scsi@...r.kernel.org>,
	Nick Piggin <npiggin@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH 1/2] brd: Fix the partitions BUG


With current code after a call to:
	bdev = blkdev_get_by_path(dev_name, mode, fs_type);
	size = i_size_read(bdev->bd_inode);
	part_size  = bdev->bd_part->nr_sects << 9;

I get the following bad results:
dev_name == /dev/ram0
  foo: [foo_mount:880] size=0x40000000 bdev=ffff88003dc24340 \
	bd_inode=ffff88003dc24430 bd_part=ffff88003ca22848 part_size=0x40000000
dev_name == /dev/ram0p1
  foo: [foo_mount:880] size=0x40000000 bdev=ffff88003d2f6d80 \
	bd_inode=ffff88003d2f6e70 bd_part=ffff88003ca22848 part_size=0x40000000
dev_name == /dev/ram0p2
  foo: [foo_mount:880] size=0x40000000 bdev=ffff88003dc24680 \
	bd_inode=ffff88003dc24770 bd_part=ffff88003ca22848 part_size=0x40000000
Note how all three bdev(s) point to the same bd_part.

This is do to a single bad clubber in brd_probe() which is
removed in this patch:
-	*part = 0;

because of this all 3 bdev(s) above get to point to the same bd_part[0]

While at it fix/rename brd_init_one() since all devices are created on
load of driver, brd_probe() will never be called with a new un-created
device.
brd_init_one() is now renamed to brd_find() which is what it does.

TODO: There is one more partitions BUG regarding
      brd_direct_access() which is fixed on the next patch.

Signed-off-by: Boaz Harrosh <boaz@...xistor.com>
---
 drivers/block/brd.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index c7d138e..92334f6 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -523,22 +523,20 @@ static void brd_free(struct brd_device *brd)
 	kfree(brd);
 }
 
-static struct brd_device *brd_init_one(int i)
+static struct brd_device *brd_find(int i)
 {
 	struct brd_device *brd;
 
 	list_for_each_entry(brd, &brd_devices, brd_list) {
 		if (brd->brd_number == i)
-			goto out;
+			return brd;
 	}
 
-	brd = brd_alloc(i);
-	if (brd) {
-		add_disk(brd->brd_disk);
-		list_add_tail(&brd->brd_list, &brd_devices);
-	}
-out:
-	return brd;
+	/* brd always allocates all its devices at load time, therefor
+	 * brd_probe will never be called with a new brd_number
+	 */
+	printk(KERN_EROR "brd: brd_find unexpected device %d\n", i);
+	return NULL;
 }
 
 static void brd_del_one(struct brd_device *brd)
@@ -554,11 +552,10 @@ static struct kobject *brd_probe(dev_t dev, int *part, void *data)
 	struct kobject *kobj;
 
 	mutex_lock(&brd_devices_mutex);
-	brd = brd_init_one(MINOR(dev) >> part_shift);
+	brd = brd_find(MINOR(dev) >> part_shift);
 	kobj = brd ? get_disk(brd->brd_disk) : NULL;
 	mutex_unlock(&brd_devices_mutex);
 
-	*part = 0;
 	return kobj;
 }
 
-- 
1.9.3


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