Re: [PATCH] fix writing to the filesystem after unmount

[Christoph Hellwig]

On Fri, Sep 08, 2023 at 12:20:14PM +0200, Jan Kara wrote:
> Well, currently you click some "Eject / safely remove / whatever" button
> and then you get a "wait" dialog until everything is done after which
> you're told the stick is safe to remove. What I imagine is that the "wait"
> dialog needs to be there while there are any (or exclusive at minimum) openers
> of the device. Not until umount(2) syscall has returned. And yes, the
> kernel doesn't quite make that easy - the best you can currently probably
> do is to try opening the device with O_EXCL and if that fails, you know
> there's some other exclusive open.

... and the simple answer to the problem is to have an event notification
for when the super_block has finally been destroyed.  That way the
application gets this notification directly instead of having to make
a process synchronous that fundamentally isn't as explained in this thread.