On 09/21/2016 10:26 PM, David Sterba wrote:
On Sat, Sep 10, 2016 at 07:03:38AM +0800, Anand Jain wrote:
 static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
 {
        struct btrfs_device *device, *tmp;
+       LIST_HEAD(pending_put);
+       INIT_LIST_HEAD(&pending_put);

LIST_HEAD declares and initializes the list to an empty one, not
necessary to call INIT_LIST_HEAD.

  Will use struct list_head makes it with inline with rest of the code.


        if (--fs_devices->opened > 0)
                return 0;
@@ -906,9 +904,24 @@ static int __btrfs_close_devices(struct btrfs_fs_devices 
*fs_devices)
        mutex_lock(&fs_devices->device_list_mutex);
        list_for_each_entry_safe(device, tmp, &fs_devices->devices, dev_list) {
                btrfs_close_one_device(device);
+               list_add(&device->dev_list, &pending_put);
        }
        mutex_unlock(&fs_devices->device_list_mutex);

+       /*
+        * btrfs_show_devname() is using the device_list_mutex,
+        * sometimes a call to blkdev_put() leads vfs calling
+        * into this func. So do put outside of device_list_mutex,
+        * as of now.
+        */
+       while (!list_empty(&pending_put)) {
+               device = list_entry(pending_put.next,

Could be list_first_entry
 ok.
+                                       struct btrfs_device, dev_list);
+               list_del(&device->dev_list);
+               btrfs_close_bdev(device);
+               call_rcu(&device->rcu, free_device);
+       }
+
        WARN_ON(fs_devices->open_devices);
        WARN_ON(fs_devices->rw_devices);
        fs_devices->opened = 0;

After this patch, the function btrfs_close_one_device no longer does
what it says, ie. it does not close the device.

 renamed to btrfs_prepare_close_one_device()

I'd have to look closer
why it allocates a new structure and replaces it in the list, but this
looks weird.

 I asked this in the ML quite sometime back. yeah reason is unknown.
 So this reason the sysfs patches (in the ML) is probably got x2
 complicated.

-Anand


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