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Subject: Re: [RESEND PATCH] mmc: core: fix race condition in
 mmc_wait_data_done
To: Ulf Hansson <ulf.hansson@linaro.org>
References: <1440731589-22241-1-git-send-email-shawn.lin@rock-chips.com>
 <55DFD4B7.3070601@rock-chips.com>
 <CAPDyKFqZXx11qsnPH_uTDptfkUFfDykNKPgVcH6AW5CbH6Fi8g@mail.gmail.com>
Cc: shawn.lin@rock-chips.com, Jialing Fu <jlfu@marvell.com>,
        linux-mmc <linux-mmc@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
From: Shawn Lin <shawn.lin@rock-chips.com>
Message-ID: <55E02F7C.1020204@rock-chips.com>
Date: Fri, 28 Aug 2015 17:53:00 +0800
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在 2015/8/28 16:55, Ulf Hansson 写道:
> On 28 August 2015 at 05:25, Shawn Lin <shawn.lin@rock-chips.com> wrote:
>> On 2015/8/28 11:13, Shawn Lin wrote:
>>>
>>> From: Jialing Fu <jlfu@marvell.com>
>>>
>>> The following panic is captured in ker3.14, but the issue still exists
>>> in latest kernel.
>>> ---------------------------------------------------------------------
>>> [   20.738217] c0 3136 (Compiler) Unable to handle kernel NULL pointer
>>> dereference
>>> at virtual address 00000578
>>> ......
>>> [   20.738499] c0 3136 (Compiler) PC is at
>>> _raw_spin_lock_irqsave+0x24/0x60
>>> [   20.738527] c0 3136 (Compiler) LR is at
>>> _raw_spin_lock_irqsave+0x20/0x60
>>> [   20.740134] c0 3136 (Compiler) Call trace:
>>> [   20.740165] c0 3136 (Compiler) [<ffffffc0008ee900>]
>>> _raw_spin_lock_irqsave+0x24/0x60
>>> [   20.740200] c0 3136 (Compiler) [<ffffffc0000dd024>] __wake_up+0x1c/0x54
>>> [   20.740230] c0 3136 (Compiler) [<ffffffc000639414>]
>>> mmc_wait_data_done+0x28/0x34
>>> [   20.740262] c0 3136 (Compiler) [<ffffffc0006391a0>]
>>> mmc_request_done+0xa4/0x220
>>> [   20.740314] c0 3136 (Compiler) [<ffffffc000656894>]
>>> sdhci_tasklet_finish+0xac/0x264
>>> [   20.740352] c0 3136 (Compiler) [<ffffffc0000a2b58>]
>>> tasklet_action+0xa0/0x158
>>> [   20.740382] c0 3136 (Compiler) [<ffffffc0000a2078>]
>>> __do_softirq+0x10c/0x2e4
>>> [   20.740411] c0 3136 (Compiler) [<ffffffc0000a24bc>] irq_exit+0x8c/0xc0
>>> [   20.740439] c0 3136 (Compiler) [<ffffffc00008489c>]
>>> handle_IRQ+0x48/0xac
>>> [   20.740469] c0 3136 (Compiler) [<ffffffc000081428>]
>>> gic_handle_irq+0x38/0x7c
>>> ----------------------------------------------------------------------
>>> Because in SMP, "mrq" has race condition between below two paths:
>>> path1: CPU0: <tasklet context>
>>>     static void mmc_wait_data_done(struct mmc_request *mrq)
>>>     {
>>>        mrq->host->context_info.is_done_rcv = true;
>>>        //
>>>        // If CPU0 has just finished "is_done_rcv = true" in path1, and at
>>>        // this moment, IRQ or ICache line missing happens in CPU0.
>>>        // What happens in CPU1 (path2)?
>>>        //
>>>        // If the mmcqd thread in CPU1(path2) hasn't entered to sleep mode:
>>>        // path2 would have chance to break from wait_event_interruptible
>>>        // in mmc_wait_for_data_req_done and continue to run for next
>>>        // mmc_request (mmc_blk_rw_rq_prep).
>>>        //
>>>        // Within mmc_blk_rq_prep, mrq is cleared to 0.
>>>        // If below line still gets host from "mrq" as the result of
>>>        // compiler, the panic happens as we traced.
>>>        wake_up_interruptible(&mrq->host->context_info.wait);
>>>     }
>>>
>>> path2: CPU1: <The mmcqd thread runs mmc_queue_thread>
>>>     static int mmc_wait_for_data_req_done(...
>>>     {
>>>        ...
>>>        while (1) {
>>>              wait_event_interruptible(context_info->wait,
>>>                      (context_info->is_done_rcv ||
>>>                       context_info->is_new_req));
>>>             static void mmc_blk_rw_rq_prep(...
>>>              {
>>>              ...
>>>              memset(brq, 0, sizeof(struct mmc_blk_request));
>>>
>>> This issue happens very coincidentally; however adding mdelay(1) in
>>> mmc_wait_data_done as below could duplicate it easily.
>>>
>>>      static void mmc_wait_data_done(struct mmc_request *mrq)
>>>      {
>>>        mrq->host->context_info.is_done_rcv = true;
>>> +    mdelay(1);
>>>        wake_up_interruptible(&mrq->host->context_info.wait);
>>>       }
>>>
>>
>> Hi, ulf
>>
>> We find this bug on Intel-C3230RK platform for very small probability.
>>
>> Whereas I can easily reproduce this case if I add a mdelay(1) or  longer
>> delay as Jialing did.
>>
>> This patch seems useful to me. Should we push it forward? :)
>
> It seems like a very good idea!
>
> Should we add a fixes tag to it?

That's cool, but how to add a fixes tag?

[Fixes] mmc: core: fix race condition in mmc_wait_data_done ?   :)

>
> [...]
>
> Kind regards
> Uffe
>
>
>


-- 
Best Regards
Shawn Lin

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