Btrfs: move kobj stuff out of dev_replace lock range

To avoid deadlock described in commit 084b6e7c7607 ("btrfs: Fix a
lockdep warning when running xfstest."), we should move kobj stuff out
of dev_replace lock range.

  "It is because the btrfs_kobj_{add/rm}_device() will call memory
  allocation with GFP_KERNEL,
  which may flush fs page cache to free space, waiting for it self to do
  the commit, causing the deadlock.

  To solve the problem, move btrfs_kobj_{add/rm}_device() out of the
  dev_replace lock range, also involing split the
  btrfs_rm_dev_replace_srcdev() function into remove and free parts.

  Now only btrfs_rm_dev_replace_remove_srcdev() is called in dev_replace
  lock range, and kobj_{add/rm} and btrfs_rm_dev_replace_free_srcdev() are
  called out of the lock range."

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
[added lockup description]
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index 02031fc..0978e52 100644 (file)
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -375,10 +375,6 @@ int btrfs_dev_replace_start(struct btrfs_root *root,
        WARN_ON(!tgt_device);
        dev_replace->tgtdev = tgt_device;
 
-       ret = btrfs_sysfs_add_device_link(tgt_device->fs_devices, tgt_device);
-       if (ret)
-               btrfs_err(root->fs_info, "kobj add dev failed %d\n", ret);
-
        printk_in_rcu(KERN_INFO
                      "BTRFS: dev_replace from %s (devid %llu) to %s started\n",
                      src_device->missing ? "<missing disk>" :
@@ -401,6 +397,10 @@ int btrfs_dev_replace_start(struct btrfs_root *root,
        args->result = BTRFS_IOCTL_DEV_REPLACE_RESULT_NO_ERROR;
        btrfs_dev_replace_unlock(dev_replace);
 
+       ret = btrfs_sysfs_add_device_link(tgt_device->fs_devices, tgt_device);
+       if (ret)
+               btrfs_err(root->fs_info, "kobj add dev failed %d\n", ret);
+
        btrfs_wait_ordered_roots(root->fs_info, -1);
 
        /* force writing the updated state information to disk */