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

[Bernd Schubert]

On 8/14/23 13:02, 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.
>
> 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?

Is there a good reason to flush O_RDONLY?


fuse: Avoid flush for O_RDONLY

From: Bernd Schubert <bschubert@xxxxxxx>

A file opened in read-only moded does not have data to be
flushed, so no need to send flush at all.

This also mitigates -EBUSY for executables, which is due to
async flush with commit 5a8bee63b1.

Fixes: 5a8bee63b1 (unless executable opened in rw)
Signed-off-by: Bernd Schubert <bschubert@xxxxxxx>


index 89d97f6188e0..e058a6af6751 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -545,7 +545,8 @@ static int fuse_flush(struct file *file, fl_owner_t id)
        if (fuse_is_bad(inode))
                return -EIO;
 
-       if (ff->open_flags & FOPEN_NOFLUSH && !fm->fc->writeback_cache)
+       if ((ff->open_flags & FOPEN_NOFLUSH && !fm->fc->writeback_cache) ||
+           ((file->f_flags & O_ACCMODE) == O_RDONLY))
                return 0;
 
        fa = kzalloc(sizeof(*fa), GFP_KERNEL);