writeback: Fix lock imbalance in writeback_sb_inodes()
writeback: Fix lock imbalance in writeback_sb_inodes()

Fix bug introduced by 169ebd90.  We have to have wb_list_lock locked when
restarting writeback loop after having waited for inode writeback.

Bug description by Ted Tso:

  I can reproduce this fairly easily by using ext4 w/o a journal, running
  under KVM with 1024megs memory, with fsstress (xfstests #13):

  [   45.153294] =====================================
  [   45.154784] [ BUG: bad unlock balance detected! ]
  [   45.155591] 3.5.0-rc1-00002-gb22b1f1 #124 Not tainted
  [   45.155591] -------------------------------------
  [   45.155591] flush-254:16/2499 is trying to release lock (&(&wb->list_lock)->rlock) at:
  [   45.155591] [<c022c3da>] writeback_sb_inodes+0x160/0x327
  [   45.155591] but there are no more locks to release!

Reported-by: Theodore Ts'o <4ed386e0495d3e109932df055831d9ec2f824927@mit.edu>
Tested-by: Theodore Ts'o <4ed386e0495d3e109932df055831d9ec2f824927@mit.edu>
Signed-off-by: Jan Kara <596727c8a0ea4db3ba2ceceedccbacd3d7b371b8@suse.cz>
Signed-off-by: Fengguang Wu <24f7fe9d205c8a9f6ade0c2894e14303ca16087f@intel.com>

TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs