Re: [REGRESSION] fuse: execve() fails with ETXTBSY due to async fuse_flush

[Bernd Schubert]

On 8/14/23 16:00, Tycho Andersen wrote:
> On Mon, Aug 14, 2023 at 01:02:35PM +0200, Miklos Szeredi wrote:
> > On Mon, 14 Aug 2023 at 08:03, Jürg Billeter <j@xxxxxxxxx> wrote:
> > > Since v6.3-rc1 commit 5a8bee63b1 ("fuse: in fuse_flush only wait if
> > > someone wants the return code") `fput()` is called asynchronously if a
> > > file is closed as part of a process exiting, i.e., if there was no
> > > explicit `close()` before exit.
> > >
> > > If the file was open for writing, also `put_write_access()` is called
> > > asynchronously as part of the async `fput()`.
> > >
> > > If that newly written file is an executable, attempting to `execve()`
> > > the new file can fail with `ETXTBSY` if it's called after the writer
> > > process exited but before the async `fput()` has run.
> >
> > Thanks for the report.
> >
> > At this point, I think it would be best to revert the original patch,
> > since only v6.4 has it.
>
> I agree.
>
> > The original fix was already a workaround, and I don't see a clear
> > path forward in this direction.  We need to see if there's better
> > direction.
> >
> > Ideas?
>
> It seems like we really do need to wait here. I guess that means we
> need some kind of exit-proof wait?


I'm not sure how hackish it is, if fuse_flush gets converted to 
queue_work() and with a new work-queue in struct fuse_inode. That 
work_queue could be flushed through a new inode operation from 
do_open_execat.


Bernd