Rafael J. Wysocki wrote:
>
> static int usermodehelper_pm_callback(struct notifier_block *nfb,
> unsigned long action,
> void *ignored)
> {
> + long retval;
> +
> switch (action) {
> case PM_HIBERNATION_PREPARE:
> case PM_SUSPEND_PREPARE:
> usermodehelper_disabled = 1;
> - return NOTIFY_OK;
> + /*
> + * From now on call_usermodehelper_exec() won't start any new
> + * helpers, so it is sufficient if running_helpers turns out to
> + * be zero at one point (it may be increased later, but that
> + * doesn't matter).
> + */
> + retval = wait_event_timeout(running_helpers_waitq,
> + atomic_read(&running_helpers) == 0,
> + RUNNING_HELPERS_TIMEOUT);
> + if (retval) {
> + return NOTIFY_OK;
> + } else {
> + usermodehelper_disabled = 0;
> + return NOTIFY_BAD;
I think this is racy. First, this needs smp_mb() between "usermodehelper_disabled = 1"
and wait_event_timeout().
Second, call_usermodehelper's path should first increment the counter, and only
then check usermodehelper_disabled, and it needs an mb() in between too. Otherwise,
the helper can see usermodehelper_disabled == 0, then PM_SUSPEND_PREPARE comes and
returns NOTIFY_OK, then the helper increments the counter and starts application.
Sadly, you can't use srcu/qrcu because it doesn't handle timeouts.
Oleg.
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