linux-kernel - Re: [PATCH] NVMe: Avoid interrupt disable during queue init.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CAGgvQNQY-9YK5i=waOE8Cext_Lp6vSGw+iofcNmaU29-_kpomw@mail.gmail.com>
Date:	Fri, 22 May 2015 23:48:41 +0530
From:	Parav Pandit <parav.pandit@...gotech.com>
To:	Keith Busch <keith.busch@...el.com>
Cc:	linux-nvme@...ts.infradead.org,
	Matthew Wilcox <willy@...ux.intel.com>,
	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] NVMe: Avoid interrupt disable during queue init.

On Fri, May 22, 2015 at 11:17 PM, Keith Busch <keith.busch@...el.com> wrote:
> On Fri, 22 May 2015, Parav Pandit wrote:
>>
>> I agree to it that nvmeq won't be null after mb(); That alone is not
>> sufficient.
>>
>> What I have proposed in previous email is,
>>
>> Converting,
>>
>> struct nvme_queue *nvmeq = dev->queues[i];
>> if (!nvmeq)
>>    continue;
>> spin_lock_irq(nvmeq->q_lock);
>>
>> to replace with,
>>
>> struct nvme_queue *nvmeq = rcu_dereference(dev->queues[i]);
>> if (!nvmeq)
>>    continue;
>> spin_lock_irq(nvmeq->q_lock);
>>
>> This will prevent fetching content of q_lock before checking for NULL
>> condition. Classic usage or RCU.
>
>
> What the heck are you talking about? The value of dev->queue_count won't
> even let the thread iterate an nvmeq before q_lock is initialized.
>
Oh, right. My bad. I was getting confused with the possible reordering
in reset path within,
nvme_free_queues()
1320                 dev->queue_count--;
1321                 dev->queues[i] = NULL;

while nvme_kthread is working on it.
But thats unlikely case because device is removed from the list before.

Yes, so mb() is good enough.
I will send you the patch.
Thanks.


> We used to rcu protect queue access, but that was to make nvme's
> make_request_fn safe to surprise removal, not for the polling thread.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/