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

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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



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