linux-kernel - Re: [REGRESSION] fuse: execve() fails with ETXTBSY due to async fuse

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Message-ID: <c88e4470-c20a-77fd-be19-f8d2e92b5125@fastmail.fm>
Date:   Mon, 14 Aug 2023 23:34:07 +0200
From:   Bernd Schubert <bernd.schubert@...tmail.fm>
To:     Tycho Andersen <tycho@...ho.pizza>,
        Miklos Szeredi <miklos@...redi.hu>
Cc:     Jürg Billeter <j@...ron.ch>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        regressions@...ts.linux.dev
Subject: Re: [REGRESSION] fuse: execve() fails with ETXTBSY due to async
 fuse_flush



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@...ron.ch> 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