From: Jon Hunter <jonathanh@nvidia.com>
To: "Dmitry Osipenko" <digetx@gmail.com>,
"Laxman Dewangan" <ldewangan@nvidia.com>,
"Vinod Koul" <vkoul@kernel.org>,
"Dan Williams" <dan.j.williams@intel.com>,
"Thierry Reding" <thierry.reding@gmail.com>,
"Michał Mirosław" <mirq-linux@rere.qmqm.pl>
Cc: <dmaengine@vger.kernel.org>, <linux-tegra@vger.kernel.org>,
<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 01/14] dmaengine: tegra-apb: Fix use-after-free
Date: Tue, 28 Jan 2020 14:02:38 +0000 [thread overview]
Message-ID: <5bbe9e3e-a64f-53be-e7f6-63e36cbae77d@nvidia.com> (raw)
In-Reply-To: <b0c85ca7-d8ac-5f9d-2c57-79543c1f9b5d@gmail.com>
On 16/01/2020 20:10, Dmitry Osipenko wrote:
> 15.01.2020 12:00, Jon Hunter пишет:
>>
>> On 14/01/2020 20:33, Dmitry Osipenko wrote:
>>> 14.01.2020 18:09, Jon Hunter пишет:
>>>>
>>>> On 12/01/2020 17:29, Dmitry Osipenko wrote:
>>>>> I was doing some experiments with I2C and noticed that Tegra APB DMA
>>>>> driver crashes sometime after I2C DMA transfer termination. The crash
>>>>> happens because tegra_dma_terminate_all() bails out immediately if pending
>>>>> list is empty, thus it doesn't release the half-completed descriptors
>>>>> which are getting re-used before ISR tasklet kicks-in.
>>>>
>>>> Can you elaborate a bit more on how these are getting re-used? What is
>>>> the sequence of events which results in the panic? I believe that this
>>>> was also reported in the past [0] and so I don't doubt there is an issue
>>>> here, but would like to completely understand this.
>>>>
>>>> Thanks!
>>>> Jon
>>>>
>>>> [0] https://lore.kernel.org/patchwork/patch/675349/
>>>>
>>>
>>> In my case it happens in the touchscreen driver during of the
>>> touchscreen's interrupt handling (in a threaded IRQ handler) + CPU is
>>> under load and there is other interrupts activity. So what happens here
>>> is that the TS driver issues one I2C transfer, which fails with
>>> (apparently bogus) timeout (because DMA descriptor is completed and
>>> removed from the pending list, but tasklet not executed yet), and then
>>> TS immediately issues another I2C transfer that re-uses the
>>> yet-incompleted descriptor. That's my understanding.
>>
>> OK, but what is the exact sequence that it allowing it to re-use the
>> incompleted descriptor?
>
> TDMA driver DMA Client
>
> 1.
> dmaengine_prep()
>
> 2.
> tegra_dma_desc_get()
> dma_desc = kzalloc()
> ...
> tegra_dma_prep_slave_sg()
> INIT_LIST_HEAD(&dma_desc->tx_list);
> INIT_LIST_HEAD(&dma_desc->cb_node);
> list_add_tail(sgreq->node,
> dma_desc->tx_list)
>
> 3.
> dma_async_issue_pending()
>
> 4.
> tegra_dma_tx_submit()
> list_splice_tail_init(dma_desc->tx_list,
> tdc->pending_sg_req)
>
> 5.
> tegra_dma_isr()
> ...
> handle_once_dma_done()
> ...
> sgreq = list_first_entry(tdc->pending_sg_req)
> list_del(sgreq->node);
> ...
> list_add_tail(dma_desc->cb_node,
> tdc->cb_desc);
> list_add_tail(dma_desc->node,
> tdc->free_dma_desc);
Isn't this the problem here, that we have placed this on the free list
before we are actually done?
It seems to me that there could still be a potential race condition
between the ISR and the tasklet running.
Jon
--
nvpublic
next prev parent reply other threads:[~2020-01-28 14:48 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-12 17:29 [PATCH v4 00/14] NVIDIA Tegra APB DMA driver fixes and improvements Dmitry Osipenko
2020-01-12 17:29 ` [PATCH v4 01/14] dmaengine: tegra-apb: Fix use-after-free Dmitry Osipenko
2020-01-14 15:09 ` Jon Hunter
2020-01-14 20:33 ` Dmitry Osipenko
2020-01-15 9:00 ` Jon Hunter
2020-01-16 20:10 ` Dmitry Osipenko
2020-01-28 14:02 ` Jon Hunter [this message]
2020-01-28 14:51 ` Dmitry Osipenko
2020-01-29 0:12 ` Dmitry Osipenko
2020-01-29 10:42 ` Jon Hunter
2020-01-12 17:29 ` [PATCH v4 02/14] dmaengine: tegra-apb: Implement synchronization callback Dmitry Osipenko
2020-01-14 15:15 ` Jon Hunter
2020-01-14 21:02 ` Dmitry Osipenko
2020-01-15 9:18 ` Jon Hunter
2020-01-15 10:25 ` Jon Hunter
2020-01-12 17:29 ` [PATCH v4 03/14] dmaengine: tegra-apb: Prevent race conditions on channel's freeing Dmitry Osipenko
2020-01-14 15:16 ` Jon Hunter
2020-01-12 17:29 ` [PATCH v4 04/14] dmaengine: tegra-apb: Clean up tasklet releasing Dmitry Osipenko
2020-01-14 15:36 ` Jon Hunter
2020-01-12 17:29 ` [PATCH v4 05/14] dmaengine: tegra-apb: Prevent race conditions of tasklet vs free list Dmitry Osipenko
2020-01-14 15:43 ` Jon Hunter
2020-01-12 17:29 ` [PATCH v4 06/14] dmaengine: tegra-apb: Use devm_platform_ioremap_resource Dmitry Osipenko
2020-01-14 15:44 ` Jon Hunter
2020-01-12 17:29 ` [PATCH v4 07/14] dmaengine: tegra-apb: Use devm_request_irq Dmitry Osipenko
2020-01-14 15:44 ` Jon Hunter
2020-01-12 17:30 ` [PATCH v4 08/14] dmaengine: tegra-apb: Fix coding style problems Dmitry Osipenko
2020-01-15 9:49 ` Jon Hunter
2020-01-16 17:37 ` Dmitry Osipenko
2020-01-28 14:05 ` Jon Hunter
2020-01-28 15:01 ` Dmitry Osipenko
2020-01-12 17:30 ` [PATCH v4 09/14] dmaengine: tegra-apb: Clean up runtime PM teardown Dmitry Osipenko
2020-01-15 9:57 ` Jon Hunter
2020-01-16 17:18 ` Dmitry Osipenko
2020-01-12 17:30 ` [PATCH v4 10/14] dmaengine: tegra-apb: Keep clock enabled only during of DMA transfer Dmitry Osipenko
2020-01-15 10:08 ` Jon Hunter
2020-01-16 17:01 ` Dmitry Osipenko
2020-01-12 17:30 ` [PATCH v4 11/14] dmaengine: tegra-apb: Clean up suspend-resume Dmitry Osipenko
2020-01-21 21:23 ` Dmitry Osipenko
2020-01-28 14:10 ` Jon Hunter
2020-01-28 14:53 ` Dmitry Osipenko
2020-01-12 17:30 ` [PATCH v4 12/14] dmaengine: tegra-apb: Add missing of_dma_controller_free Dmitry Osipenko
2020-01-15 10:10 ` Jon Hunter
2020-01-12 17:30 ` [PATCH v4 13/14] dmaengine: tegra-apb: Allow to compile as a loadable kernel module Dmitry Osipenko
2020-01-15 10:10 ` Jon Hunter
2020-01-12 17:30 ` [PATCH v4 14/14] dmaengine: tegra-apb: Remove MODULE_ALIAS Dmitry Osipenko
2020-01-15 10:11 ` Jon Hunter
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