linux-kernel - Re: ETXTBSY window in _

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Message-ID: <0a372029-9a31-54c3-4d8a-8a9597361955@ispras.ru>
Date: Wed, 27 Aug 2025 10:22:14 +0300 (MSK)
From: Alexander Monakov <amonakov@...ras.ru>
To: Al Viro <viro@...iv.linux.org.uk>
cc: linux-fsdevel@...r.kernel.org, Christian Brauner <brauner@...nel.org>, 
    Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org
Subject: Re: ETXTBSY window in __fput

On Tue, 26 Aug 2025, Al Viro wrote:

> Egads...  Let me get it straight - you have a bunch of threads sharing descriptor
> tables and some of them are forking (or cloning without shared descriptor tables)
> while that is going on?

I suppose if they could start a new process in a more straightforward manner,
they would. But you cannot start a new process without fork. Anyway, I'm but
a messenger here: the problem has been hit by various people in the Go community
(and by Go team itself, at least twice). Here I'm asking about a potential
shortcoming in __fput that exacerbates the problem.

> Frankly, in such situation I would spawn a thread for that, did unshare(CLONE_FILES)
> in it, replaced the binary and buggered off, with parent waiting for it to complete.

Good to know, but it doesn't sound very efficient (and like something that could be
integrated in Go runtime).

Anyhow, if the alleged race window in __fput is real, why not close it for good?

Alexander