linux-kernel - Infinite loop in get_file_rcu() in face of a saturated ref count

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Message-ID: <CAGudoHHBRhU+XidV9U4osc2Ta4w0Lgi2XiFkYukKQoH45zT6vw@mail.gmail.com>
Date: Mon, 25 Aug 2025 23:43:00 +0200
From: Mateusz Guzik <mjguzik@...il.com>
To: Christian Brauner <brauner@...nel.org>
Cc: linux-fsdevel <linux-fsdevel@...r.kernel.org>, 
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Infinite loop in get_file_rcu() in face of a saturated ref count

__get_file_rcu() bails early:

        if (unlikely(!file_ref_get(&file->f_ref)))
                return ERR_PTR(-EAGAIN);

But get_file_rcu():
       for (;;) {
                struct file __rcu *file;

                file = __get_file_rcu(f);
                if (!IS_ERR(file))
                        return file;
        }

So if this encounters a saturated refcount, the loop with never end.

I don't know what makes the most sense to do here and I'm no position
to mess with any patches.

This is not a serious problem either, so I would put this on the back
burner. Just reporting for interested.
-- 
Mateusz Guzik <mjguzik gmail.com>