On Wed, 8 Jun 2011 08:20:57 +0800 Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote: > On Wed, Jun 08, 2011 at 07:03:19AM +0800, Andrew Morton wrote: > > On Wed, 08 Jun 2011 05:32:43 +0800 > > Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote: > > > > > static void bdev_inode_switch_bdi(struct inode *inode, > > > struct backing_dev_info *dst) > > > { > > > - spin_lock(&inode_wb_list_lock); > > > + struct backing_dev_info *old = inode->i_data.backing_dev_info; > > > + > > > + if (unlikely(dst == old)) /* deadlock avoidance */ > > > + return; > > > > Why does this occur? > > That's a fix from Hugh Dickins: yes, I remember it. And I remember rubberiness about this at the time ;) > Yesterday's mmotm hangs at startup, and with lockdep it reports: > BUG: spinlock recursion on CPU#1, blkid/284 - with bdi_lock_two() > called from bdev_inode_switch_bdi() in the backtrace. It appears > that this function is sometimes called with new the same as old. > > The problem becomes clear when looking at bdi_lock_two(), which will > immediately deadlock itself if called with (wb1 == wb2): > > void bdi_lock_two(struct bdi_writeback *wb1, struct bdi_writeback *wb2) > { > if (wb1 < wb2) { > spin_lock(&wb1->list_lock); > spin_lock_nested(&wb2->list_lock, 1); > } else { > spin_lock(&wb2->list_lock); > spin_lock_nested(&wb1->list_lock, 1); > } > } But why are we asking bdev_inode_switch_bdi() to switch an inode to a bdi where it already resides? -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html