Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion

From: Al Viro
Date: Wed Sep 13 2017 - 19:04:35 EST

On Wed, Sep 13, 2017 at 01:09:41PM -0700, Jaegeuk Kim wrote:
> + if (!retval && (flags & UMOUNT_WAIT)) {
> + if (likely(!(current->flags & PF_KTHREAD)))
> + task_work_run();

This is complete crap. The same damn thing will be done by
caller of sys_umount() pretty much immediately afterwards.
I'm not sure what it is that you are trying to paper over,
but this is just plain wrong.

What _is_ the semantics of UMOUNT_WAIT? What does it guarantee,
and what would be supplying it to umount(2)?