Hello,
My static analysis tool reports a possible deadlock in the tty driver in
Linux 5.10:
uart_remove_one_port()
mutex_lock(&port->mutex); --> Line 3017 (Lock A)
wait_event(state->remove_wait, ...); --> Line 3019 (Wait X)
mutex_unlock(&port->mutex); --> Line 3021 (Unlock A)
uart_hangup()
mutex_lock(&port->mutex); --> Line 1667 (Lock A)
uart_flush_buffer()
uart_port_unlock()
uart_port_deref()
wake_up(&uport->state->remove_wait); --> Line 68 (Wake X)
mutex_unlock(&port->mutex); --> Line 1684 (Unlock A)
When uart_remove_one_port() is executed, "Wait X" is performed by
holding "Lock A". If uart_hangup() is executed at this time, "Wake X"
cannot be performed to wake up "Wait X" in uart_remove_one_port(),
because "Lock A" has been already hold by uart_remove_one_port(),
causing a possible deadlock.
I am not quite sure whether this possible problem is real and how to fix
it if it is real.
Maybe we can call wait_event() before mutex_lock() in
uart_remove_one_port().
Any feedback would be appreciated, thanks :)
Best wishes,
Jia-Ju Bai
