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Btrfs: avoid races between super writeout and device list updates

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On multi-device filesystems, btrfs writes supers to all of the devices
before considering a sync complete.  There wasn't any additional
locking between super writeout and the device list management code
because device management was done inside a transaction and
super writeout only happened  with no transation writers running.

With the btrfs fsync log and other async transaction updates, this
has been racey for some time.  This adds a mutex to protect
the device list.  The existing volume mutex could not be reused due to
transaction lock ordering requirements.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Chris Mason
2009-06-10 15:17:02 -04:00
parent 7df336ec12
commit e5e9a5206a
3 changed files with 45 additions and 2 deletions
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6
fs/btrfs/disk-io.c
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@@ -2111,7 +2111,7 @@ static int write_dev_supers(struct btrfs_device *device,
int write_all_supers(struct btrfs_root *root, int max_mirrors)
{
struct list_head *head = &root->fs_info->fs_devices->devices;
struct list_head *head;
struct btrfs_device *dev;
struct btrfs_super_block *sb;
struct btrfs_dev_item *dev_item;
@@ -2126,6 +2126,9 @@ int write_all_supers(struct btrfs_root *root, int max_mirrors)
sb = &root->fs_info->super_for_commit;
dev_item = &sb->dev_item;
mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
head = &root->fs_info->fs_devices->devices;
list_for_each_entry(dev, head, dev_list) {
if (!dev->bdev) {
total_errors++;
@@ -2169,6 +2172,7 @@ int write_all_supers(struct btrfs_root *root, int max_mirrors)
if (ret)
total_errors++;
}
mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
if (total_errors > max_errors) {
printk(KERN_ERR "btrfs: %d errors while writing supers\n",
total_errors);