linux-kernel - Re: ata: BUG in ata_sff_hsm

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Date:	Fri, 29 Jan 2016 12:59:49 +0100
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-ide@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Jeff Garzik <jgarzik@...hat.com>,
	Sergei Shtylyov <sshtylyov@...mvista.com>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: ata: BUG in ata_sff_hsm_move

On Fri, Jan 29, 2016 at 12:52 PM, Tejun Heo <tj@...nel.org> wrote:
> 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.

Here are two logs, in both cases no kernel messages prior to the bug:
https://gist.githubusercontent.com/dvyukov/5087d633e3620280b6c7/raw/31c9ab1ced92ac5f85cfb15eaf48ec5793c2c3a1/gistfile1.txt
https://gist.githubusercontent.com/dvyukov/825b2e3d5fb80ae08a9a/raw/03c5a4f4c4bd9d0a304a71cda2da4c92f4b7f1ba/gistfile1.txt