With this patch, I am starting to have issues running fsck immediately after umount. *** fsck.ext4 output *** fsck from util-linux-ng 2.17.2 e2fsck 1.42.12-gg3 (9-Sep-2014) Warning! /dev/sdb3 is in use. Pass 1: Checking inodes, blocks, and sizes Deleted inode 62346243 has zero dtime. Fix? no On Wed, Feb 17, 2016 at 2:30 PM, Jan Kara <jack@xxxxxxx> wrote: > On Wed 17-02-16 16:07:44, Tejun Heo wrote: >> Hello, Jan. >> >> On Wed, Feb 17, 2016 at 09:57:21PM +0100, Jan Kara wrote: >> > Well, but this has the side-effect that trying to umount a filesystem while >> > migrations are happening will result in EBUSY error. Without obvious reason >> > why that happens. As an admin I would be rather upset when umount sometimes >> > returns EBUSY without apparent reason and you have to basically implement a >> > loop around umount to make it reliable. So a nack from me for this patch. >> >> I see. Can you please point me to the s_active check during umount? >> I first tried s_umount but couldn't transfer its ownership to the >> worker so ended up doing s_active. I looked at how s_active is used >> and couldn't find where it'd block umount. may_umount() checks >> mnt_count, not s_active, so it looked like holding s_active may delay >> destruction of the superblock but not prevent umount. > > Bah, sorry. It's too late here. You are right that s_active will just delay > destruction of the superblock until the reference is dropped. So I don't > see obvious issues with what you do and I retract my nack. I still feel > somewhat uneasy about postponing fs shutdown to a workqueue like this but > hopefully there's no hidden catch. > > Honza > > >> > Traditionally, we have used sb->s_count and sb->s_umount semaphore to pin >> > superblock while writeback code was working on it. That makes umount block >> > until we can safely unmount the filesystem and thus doesn't result in these >> > spurious EBUSY errors. But from a quick look this can be problematic for the >> > cgroup setting. >> > >> > Alternatively, you could either cancel all the switching work when >> > unmounting filesystem or maybe just handle I_WB_SWITCH similarly to I_SYNC >> > - don't grab inode reference when switching is going on, just make >> > I_WB_SWITCH pin the inode and wait in evict() for it to be clear (similarly >> > as we call inode_wait_for_writeback() there). >> >> Yeah, this is an alternative but likely more involved. >> >> Thanks. >> >> -- >> tejun > -- > Jan Kara <jack@xxxxxxxx> > SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
