On 04/14/2016 05:10 PM, Yauhen Kharuzhy wrote:
On Thu, Apr 14, 2016 at 02:59:23PM +0800, Anand Jain wrote:
Hi Yauhen
On 04/14/2016 09:15 AM, Yauhen Kharuzhy wrote:
fs_info->sb->s_bdev field isn't set to any value at mount time
There were patch to do set it at the vfs layer, or something like that.
but is set
after device replacing or at device closing.
Actually we are updating s_bdev/latest_bdev wrongly at most of
the device related operations, and not just here. I had plans
of wrapping all those into a common helper function and separate
from this patch set, when time permits, I am ok if you are fixing
all those.
Thanks, Anand
Yes, I can but I need to know expected behaviour. Should we set a s_bdev
field (as proposed in my patch) or we can keep it NULL because btrfs has
its own sync implementation and non-NULL value has no sense with multi-device
FS?
I am not completely sure, I need to dig. But I think.. and suggest
not to change s_bdev mainly because..
For ext4 vfs sets the s_bdev (yeah we use mount_fs() instead).
And also at
https://lwn.net/Articles/379862/
it is clear that originally we have had plans to maintain s_bdev
as NULL.
But that's too old, and there were some patches to handle multi
device in the vfs layer, it needs a review of that part which
I am not sure.
In any case, its better to have one fix per patch, and about
s_bdev its distinctly a candidate for a newer analysis and
patch fix.
Actually s_bdev is changed in two locations only: after device replace
and at device closing. At device replace we always (I hope...) may suppose that
target device's bdev is valid, so we need to change behaviour of
device_force_close() only.
I will do something like this..
-----
- if (fs_info->sb->s_bdev == src_device->bdev)
+ if (fs_info->sb->s_bdev &&
+ (fs_info->sb->s_bdev == src_device->bdev))
fs_info->sb->s_bdev = tgt_device->bdev;
-----
so that we won't have s_bdev set to something after replacing
a missing or failed. And move them to a helper function.
Thanks, Anand
But I still didn't check latest_bdev exactly meaning.
In any case, I will try to help to make global spare code stable first.
Existing code of
device_force_close() checks if current s_bdev is not equal to closing
bdev and, if equal, replace it by bdev field of first btrfs_device from
device list. This device may be the same as closed, and s_bdev field will
be invalid.
If s_bdev is not NULL but references an freed block device, kernel
oopses at filesystem sync time on unmount.
For multi-device FS setting of this field may be senseless, but using of
it should be consistent over the all btrfs code. So, set it on mount
time and select valid device at device closing time.
Alternative solution may be to not set s_bdev entirely.
Signed-off-by: Yauhen Kharuzhy <yauhen.kharu...@zavadatar.com>
---
fs/btrfs/super.c | 1 +
fs/btrfs/volumes.c | 16 ++++++++++++----
2 files changed, 13 insertions(+), 4 deletions(-)
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 3dd154e..1a2c58f 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1522,6 +1522,7 @@ static struct dentry *btrfs_mount(struct file_system_type
*fs_type, int flags,
char b[BDEVNAME_SIZE];
strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id));
+ s->s_bdev = bdev;
btrfs_sb(s)->bdev_holder = fs_type;
error = btrfs_fill_super(s, fs_devices, data,
flags & MS_SILENT ? 1 : 0);
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 08ab116..f14f3f2 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -7132,6 +7132,7 @@ void device_force_close(struct btrfs_device *device)
{
struct btrfs_device *next_device;
struct btrfs_fs_devices *fs_devices;
+ int found = 0;
fs_devices = device->fs_devices;
@@ -7139,13 +7140,20 @@ void device_force_close(struct btrfs_device *device)
mutex_lock(&fs_devices->fs_info->chunk_mutex);
spin_lock(&fs_devices->fs_info->free_chunk_lock);
- next_device = list_entry(fs_devices->devices.next,
- struct btrfs_device, dev_list);
+ list_for_each_entry(next_device, &fs_devices->devices, dev_list) {
+ if (next_device->bdev && next_device->bdev != device->bdev) {
+ found = 1;
+ break;
+ }
+ }
+
if (device->bdev == fs_devices->fs_info->sb->s_bdev)
- fs_devices->fs_info->sb->s_bdev = next_device->bdev;
+ fs_devices->fs_info->sb->s_bdev =
+ found ? next_device->bdev : NULL;
if (device->bdev == fs_devices->latest_bdev)
- fs_devices->latest_bdev = next_device->bdev;
+ fs_devices->latest_bdev =
+ found ? next_device->bdev : NULL;
if (device->bdev)
fs_devices->open_devices--;
--
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