Re: [PATCH v19 2/7] driver core: Prevent device_add() during system shutdown

[sashiko-bot@kernel.org]

> In Async device shutdown, device_kset->list lock is released to handle
> asynchronisation and hold again to get entry from device_kset->list.
> Which will leave window when device_add can try to add the device to
> device_kset list and temper with ongoing shutdown process. New added
> device can be async type or sync type and might also introduce new
> dependency which can cause device_shutdown path to deadlock. S is
> waiting C to finish but C is never scheduled as it was added recently
> from device_add path. And C can only be scheduled when main loops
> continue to reach to C which is waiting on S.
> 
> So, When a system enters shutdown (SYSTEM_HALT, SYSTEM_POWER_OFF, or
> SYSTEM_RESTART), new devices should not be allowed to be added.
> Adding system_state check (system_is_shutting_down()) to avoid
> device_add incase of these states of the system.
> 
> While device_add() performs an initial check of system_is_shutting_down(),
> a race window exists between this initial check and kobject_add(),
> during which device_shutdown() may already be scanning devices_kset->list.
> If device_shutdown() passes the device after kobject_add() registers it
> onto devices_kset->list, device_add() would otherwise complete device
> initialization and driver matching, leaving an active device running
> after system shutdown finishes.
> 
> Fix this TOCTOU race by re-checking system_is_shutting_down() under
> devices_kset->list_lock right after kobject_add().
> 
> Signed-off-by: Tarun Sahu <tarunsahu@google.com>
> Signed-off-by: David Jeffery <djeffery@redhat.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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