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From:   Konstantin Khorenko <khorenko@virtuozzo.com>
To:     Jessica Yu <jeyu@kernel.org>, Prarit Bhargava <prarit@redhat.com>,
        Barret Rhoden <brho@google.com>
Cc:     Konstantin Khorenko <khorenko@virtuozzo.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        linux-kernel@vger.kernel.org, David Arcari <darcari@redhat.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>
Subject: [PATCH 1/1] kernel/module.c: wakeup processes in module_wq on module unload
Date:   Wed, 13 Nov 2019 12:29:50 +0300
Message-Id: <20191113092950.15556-2-khorenko@virtuozzo.com>
In-Reply-To: <20191113092950.15556-1-khorenko@virtuozzo.com>
References: <20191113092950.15556-1-khorenko@virtuozzo.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Fix the race between load and unload a kernel module.

sys_delete_module()
 try_stop_module()
  mod->state = _GOING
					add_unformed_module()
					 old = find_module_all()
					 (old->state == _GOING =>
					  wait_event_interruptible())

					 During pre-condition
					 finished_loading() rets 0
					 schedule()
					 (never gets waken up later)
 free_module()
  mod->state = _UNFORMED
   list_del_rcu(&mod->list)
   (dels mod from "modules" list)

return

The race above leads to modprobe hanging forever on loading
a module.

Error paths on loading module call wake_up_all(&module_wq) after
freeing module, so let's do the same on straight module unload.

Fixes: 6e6de3dee51a ("kernel/module.c: Only return -EEXIST
for modules that have finished loading")

Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com>
---
 kernel/module.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/module.c b/kernel/module.c
index ff2d7359a418..cb09a5f37a5f 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1033,6 +1033,8 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
 	strlcpy(last_unloaded_module, mod->name, sizeof(last_unloaded_module));
 
 	free_module(mod);
+	/* someone could wait for the module in add_unformed_module() */
+	wake_up_all(&module_wq);
 	return 0;
 out:
 	mutex_unlock(&module_mutex);
-- 
2.15.1