[PATCH] Btrfs: fix oops when calling statfs on readonly device

[PATCH] Btrfs: fix oops when calling statfs on readonly device

[Li Zefan]

To reproduce this bug:

  # dd if=/dev/zero of=img bs=1M count=256
  # mkfs.btrfs img
  # losetup -r /dev/loop1 img
  # mount /dev/loop1 /mnt
  OOPS!!

It triggered BUG_ON(!nr_devices) in btrfs_calc_avail_data_space().

To fix this, instead of checking write-only devices, we check all open
deivces:

  # df -h /dev/loop1
  Filesystem            Size  Used Avail Use% Mounted on
  /dev/loop1            250M   28K  238M   1% /mnt

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 fs/btrfs/super.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 8bd9d6d..1a3ce9e 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1083,7 +1083,7 @@ static int btrfs_calc_avail_data_space(struct btrfs_root *root, u64 *free_bytes)
 	int i = 0, nr_devices;
 	int ret;
 
-	nr_devices = fs_info->fs_devices->rw_devices;
+	nr_devices = fs_info->fs_devices->open_devices;
 	BUG_ON(!nr_devices);
 
 	devices_info = kmalloc(sizeof(*devices_info) * nr_devices,
@@ -1105,8 +1105,8 @@ static int btrfs_calc_avail_data_space(struct btrfs_root *root, u64 *free_bytes)
 	else
 		min_stripe_size = BTRFS_STRIPE_LEN;
 
-	list_for_each_entry(device, &fs_devices->alloc_list, dev_alloc_list) {
-		if (!device->in_fs_metadata)
+	list_for_each_entry(device, &fs_devices->devices, dev_list) {
+		if (!device->in_fs_metadata || !device->bdev)
 			continue;
 
 		avail_space = device->total_bytes - device->bytes_used;
-- 1.7.3.1 

Re: [PATCH] Btrfs: fix oops when calling statfs on readonly device

[David Sterba]

On Mon, Nov 28, 2011 at 04:43:00PM +0800, Li Zefan wrote:
> To reproduce this bug:
> 
>   # dd if=/dev/zero of=img bs=1M count=256
>   # mkfs.btrfs img
>   # losetup -r /dev/loop1 img
>   # mount /dev/loop1 /mnt
>   OOPS!!
> 
> It triggered BUG_ON(!nr_devices) in btrfs_calc_avail_data_space().

FYI, A patch fixing this has been sent long ago but the was not picked
up. I have collected and pushed it to Chris last week.

http://lkml.indiana.edu/hypermail/linux/kernel/1108.0/00157.html

> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -1083,7 +1083,7 @@ static int btrfs_calc_avail_data_space(struct btrfs_root *root, u64 *free_bytes)
>  	int i = 0, nr_devices;
>  	int ret;
>  
> -	nr_devices = fs_info->fs_devices->rw_devices;
> +	nr_devices = fs_info->fs_devices->open_devices;
>  	BUG_ON(!nr_devices);

This what the referenced patch does ...

>  
>  	devices_info = kmalloc(sizeof(*devices_info) * nr_devices,
> @@ -1105,8 +1105,8 @@ static int btrfs_calc_avail_data_space(struct btrfs_root *root, u64 *free_bytes)
>  	else
>  		min_stripe_size = BTRFS_STRIPE_LEN;
>  
> -	list_for_each_entry(device, &fs_devices->alloc_list, dev_alloc_list) {
> -		if (!device->in_fs_metadata)
> +	list_for_each_entry(device, &fs_devices->devices, dev_list) {
> +		if (!device->in_fs_metadata || !device->bdev)
>  			continue;

... but misses this part, so you patch is more complete and should be
picked instead.


david