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SubjectRe: [PATCH 1/1] kernel/module.c: wakeup processes in module_wq on module unload
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On 11/13/19 4:29 AM, Konstantin Khorenko wrote:
> 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);

free_module() acts on that *this* module so it makes sense to include the
wake_up_all(&module_wq) call in delete_module. IIRC I did try a module load &
unload stress test but it looks like my testing wasn't hard enough :(

In any case,

Reviewed-by: Prarit Bhargava <prarit@redhat.com>

P.

> return 0;
> out:
> mutex_unlock(&module_mutex);
>

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