Hello, Dmitry.

On Thu, Jan 28, 2016 at 12:35:43PM +0100, Dmitry Vyukov wrote:

Hello,

I episodically hit the following BUG while running syzkaller fuzzer:

ata2: protocol 2 task_state 0 (dev_stat 0x41)
------------[ cut here ]------------
kernel BUG at drivers/ata/libata-sff.c:1302!

...

So the unexpected state is HSM_IDLE.

Hmmm... the port interrupt handler checks for IDLE before calling into
hsm_move, so the only explanation would be that something is resetting
it to IDLE inbetween.  ce7514526742 ("libata: prevent HSM state change
race between ISR and PIO") describes and fixes the same problem.  The
fix seems correct and I can't find anywhere else where this can
happen.  :(

Can you please post the kernel log leading to the BUG?  Also, I don't
think that condition needs to be BUG.  I'll change it to WARN.

Thanks.

-- 
tejun