On Sat, Mar 09, 2013 at 07:17:04AM -0700, Eric Sandeen wrote: > On 3/9/13 6:27 AM, Chris Mason wrote: > > On Fri, Mar 08, 2013 at 10:23:01PM -0700, Eric Sandeen wrote: > >> Doing this would reliably fail with -EBUSY for me: > >> > >> # mount /dev/sdb2 /mnt/scratch; umount /mnt/scratch; mkfs.btrfs -f /dev/sdb2 > >> ... > >> unable to open /dev/sdb2: Device or resource busy > >> > >> because mkfs.btrfs tries to open the device O_EXCL, and somebody still has it. > >> > >> Using systemtap to track bdev gets & puts shows a kworker thread doing a > >> blkdev put after mkfs attempts a get; this is left over from the unmount. > >> > >> Adding an rcu_barrier() to btrfs_close_devices() causes unmount to wait > >> until all blkdev_put()s are done, and the device is truly free once > >> unmount completes. > > > > Thanks for tracking this down Eric. > > Sure thing, sorry it took so long. > > > Is this kworker triggered by btrfs > > or is this something we should be doing for the other filesystems too? > > It's all btrfs ;) > > btrfs_close_devices > __btrfs_close_devices > call_rcu(&device->rcu, free_device); > free_device > INIT_WORK(&device->rcu_work, __free_device); > schedule_work(&device->rcu_work); > Great, that makes a ton more sense. I'm a little confused on why we're seeing it so much more now than in the past. > > The behavior came from: > > commit 1f78160ce1b1b8e657e2248118c4d91f881763f0 > Author: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxx> > Date: Wed Apr 20 10:09:16 2011 +0000 > > Btrfs: using rcu lock in the reader side of devices list > > Anyway, I can send V2 in close_ctree if you like. Thinking about it more > though, btrfs_close_devices is closer to the action, so now I think > I'd leave it there. :) > > I probably should have put a comment in to say what the heck it's for, > too. Feel free to fix on merge or I can send another patch. Ok, please add the comment and a cc to stable. Thanks again. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
