Re: [RESEND PATCH] mmc: core: fix race condition in mmc_wait_data_done

[Shawn Lin]

å 2015/8/28 16:55, Ulf Hansson åé:
> On 28 August 2015 at 05:25, Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> wrote:
> > On 2015/8/28 11:13, Shawn Lin wrote:
> > > From: Jialing Fu <jlfu@xxxxxxxxxxx>
> > >
> > > 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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