tree 841ce0af67dfaef41e5297fdbfa52255a1343f0b
parent 250f8e3db646028353a2a737ddb7a894c97a1098
author Wu Fengguang <fengguang.wu@intel.com> 1311999275 -0600
committer Wu Fengguang <fengguang.wu@intel.com> 1312123928 +0800

don't busy retry the inode on failed grab_super_passive()

This fixes a soft lockup on conditions

a) the flusher is working on a work by __bdi_start_writeback(), while

b) someone else calls writeback_inodes_sb*() or sync_inodes_sb(), which
   grab sb->s_umount and enqueue a new work for the flusher to execute

The s_umount grabbed by (b) will fail the grab_super_passive() in (a).
Then if the inode is requeued, wb_writeback() will busy retry on it.
As a result, wb_writeback() loops for ever without releasing
wb->list_lock, which further blocks other tasks.

Fix the busy loop by redirtying the inode. This may undesirably delay
the writeback of the inode, however most likely it will be picked up
soon by the queued work by writeback_inodes_sb*(), sync_inodes_sb() or
even writeback_inodes_wb().

bug url: http://www.spinics.net/lists/linux-fsdevel/msg47292.html

Reported-by: Christoph Hellwig <hch@infradead.org>
Tested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>