From: Timur Tabi <timur@codeaurora.org>
To: Stanimir Varbanov <stanimir.varbanov@linaro.org>,
linux-arm-kernel@lists.infradead.org,
linux-crypto@vger.kernel.org, vinod.koul@linaro.org,
Matt Mackall <mpm@selenic.com>,
swboyd@chromium.org, linux-arm-msm@vger.kernel.org,
timur@kernel.org
Subject: Re: [PATCH 1/2] hwrng: msm: add a spinlock and support for blocking reads
Date: Fri, 22 Jun 2018 10:41:11 -0500 [thread overview]
Message-ID: <6d655b97-418e-bacf-7e88-b9179cdc6fd1@codeaurora.org> (raw)
In-Reply-To: <acc7e9d3-8a81-ff15-27c7-78ec7c17f6cc@linaro.org>
On 6/22/18 10:38 AM, Stanimir Varbanov wrote:
> Before entering into the read function we already hold a mutex which
> serializes data reading so I cannot imagine how below sequence could
> happen. Can you explain how to reproduce this race?
>
>> 1. Core 1 reads status register, shows data is available.
>> 2. Core 2 also reads status register, same result
>> 3. Core 2 reads data register, depleting all entropy
>> 4. Core 1 reads data register, which returns 0
I have a test which spawns 100 copies of rngtest on a 48-core machine.
Without the spinlock, the driver returns no data much more often.
If there really is a mutex that serializes data reads across all cores,
then I don't have an explanation.
--
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm
Technologies, Inc. Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.
next prev parent reply other threads:[~2018-06-22 15:41 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-21 15:17 [PATCH 1/2] hwrng: msm: add a spinlock and support for blocking reads Timur Tabi
2018-06-21 15:17 ` [PATCH 2/2] hwrng: msm: add ACPI support Timur Tabi
2018-06-22 4:23 ` Vinod
2018-06-22 4:26 ` Timur Tabi
2018-06-22 4:44 ` Vinod
2018-06-22 4:46 ` Timur Tabi
2018-06-22 4:48 ` Vinod
2018-06-22 4:17 ` [PATCH 1/2] hwrng: msm: add a spinlock and support for blocking reads Vinod
2018-06-22 4:18 ` Timur Tabi
2018-06-22 4:24 ` Vinod
2018-06-22 4:28 ` Timur Tabi
2018-06-22 5:36 ` Stephen Boyd
2018-06-22 13:11 ` Timur Tabi
2018-06-22 15:38 ` Stanimir Varbanov
2018-06-22 15:41 ` Timur Tabi [this message]
2018-06-22 17:51 ` Stephen Boyd
2018-06-22 18:03 ` Timur Tabi
2018-06-22 21:17 ` Timur Tabi
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