Re: possible deadlock in ppp_dev_uninit

[Guillaume Nault]

On Fri, Jan 05, 2018 at 07:15:31PM +0100, Guillaume Nault wrote:
> That's probably worth a test anyway.
>
Copy/paste error :-/

Here's a version that should apply cleanly.

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git master

-------- 8< --------

diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index d8e5747ff4e3..264d4af0bf69 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -1006,17 +1006,18 @@ static int ppp_unit_register(struct ppp *ppp, int unit, 
bool ifname_is_set)
        if (!ifname_is_set)
                snprintf(ppp->dev->name, IFNAMSIZ, "ppp%i", ppp->file.index);
 
+       mutex_unlock(&pn->all_ppp_mutex);
+
        ret = register_netdevice(ppp->dev);
        if (ret < 0)
                goto err_unit;
 
        atomic_inc(&ppp_unit_count);
 
-       mutex_unlock(&pn->all_ppp_mutex);
-
        return 0;
 
 err_unit:
+       mutex_lock(&pn->all_ppp_mutex);
        unit_put(&pn->units_idr, ppp->file.index);
 err:
        mutex_unlock(&pn->all_ppp_mutex);