From e5e9a5206a171b2c467e494aebcdcf70c47289bc Mon Sep 17 00:00:00 2001 From: Chris Mason Date: Wed, 10 Jun 2009 15:17:02 -0400 Subject: Btrfs: avoid races between super writeout and device list updates 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 --- fs/btrfs/disk-io.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'fs/btrfs/disk-io.c') diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index 6c54c210dfd..b7ddc77fa56 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -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); -- cgit v1.2.3