From 0e995816f4fb69cef602b7fe82da68ced6be3b41 Mon Sep 17 00:00:00 2001 From: Wu Fengguang Date: Fri, 29 Jul 2011 22:14:35 -0600 Subject: 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 Tested-by: Christoph Hellwig Signed-off-by: Wu Fengguang --- fs/fs-writeback.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 1599aa985fe2..04cf3b91e501 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -618,7 +618,12 @@ static long __writeback_inodes_wb(struct bdi_writeback *wb, struct super_block *sb = inode->i_sb; if (!grab_super_passive(sb)) { - requeue_io(inode, wb); + /* + * grab_super_passive() may fail consistently due to + * s_umount being grabbed by someone else. Don't use + * requeue_io() to avoid busy retrying the inode/sb. + */ + redirty_tail(inode, wb); continue; } wrote += writeback_sb_inodes(sb, wb, work); -- cgit v1.2.3