...

And then we get to pid 858. This is in set_device_name(), which

was called from led_trigger_set() and led_trigger_register().

We know from pid 663 that led_trigger_register() can take a read

on leds_list_lock, and indeed it does and then calls

led_match_default_trigger(), which then goes on to call

led_trigger_set(). Bingo, this is why pid 666 is blocked, which

then blocks pid 663. pid 663 takes the rtnl lock, which blocks

everything else _and_ also blocks pid 858 in set_device_name().

Lockdep would've found this... this is a classic AB-BA deadlock

between the leds_list_lock rwsem and the rtnl mutex.

I haven't checked to see how that deadlock got introduced, that's

for someone else to do.

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