Re: ETXTBSY window in __fput

[Alexander Monakov <amonakov@ispras.ru>]

On Wed, 27 Aug 2025, Alexander Monakov wrote:

> Dear fs hackers,
> 
> I suspect there's an unfortunate race window in __fput where file locks are
> dropped (locks_remove_file) prior to decreasing writer refcount
> (put_file_access). If I'm not mistaken, this window is observable and it
> breaks a solution to ETXTBSY problem on exec'ing a just-written file, explained
> in more detail below.

The race in __fput is a problem irrespective of how the testcase triggers it,
right? It's just showing a real-world scenario. But the issue can be
demonstrated without a multithreaded fork: imagine one process placing an
exclusive lock on a file and writing to it, another process waiting on that
lock and immediately execve'ing when the lock is released.

Can put_file_access be moved prior to locks_remove_file in __fput?

Alexander