linux-kernel - Re: [PATCH v2] bus: mhi: host: Fix race between channel preparation and M0 event

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Date:   Fri, 28 Oct 2022 22:24:01 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Qiang Yu <quic_qianyu@...cinc.com>
Cc:     mani@...nel.org, loic.poulain@...aro.org, mhi@...ts.linux.dev,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        quic_cang@...cinc.com, mrana@...cinc.com
Subject: Re: [PATCH v2] bus: mhi: host: Fix race between channel preparation
 and M0 event

On Sun, Oct 16, 2022 at 11:05:32AM +0800, Qiang Yu wrote:
> There is a race condition where mhi_prepare_channel() updates the
> read and write pointers as the base address and in parallel, if
> an M0 transition occurs, the tasklet goes ahead and rings
> doorbells for all channels with a delta in TRE rings assuming
> they are already enabled. This causes a null pointer access. Fix
> it by adding a channel enabled check before ringing channel
> doorbells.
> 
> Fixes: a6e2e3522f29 "bus: mhi: core: Add support for PM state transitions"
> Signed-off-by: Qiang Yu <quic_qianyu@...cinc.com>

Can you also CC stable list for backporting?

Reviewed-by: Manivannan Sadhasivam <mani@...nel.org>

Thanks,
Mani

> ---
> v1->v2: add Fixes tags
> 
>  drivers/bus/mhi/host/pm.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/bus/mhi/host/pm.c b/drivers/bus/mhi/host/pm.c
> index 4a42186..0834590 100644
> --- a/drivers/bus/mhi/host/pm.c
> +++ b/drivers/bus/mhi/host/pm.c
> @@ -301,7 +301,8 @@ int mhi_pm_m0_transition(struct mhi_controller *mhi_cntrl)
>  		read_lock_irq(&mhi_chan->lock);
>  
>  		/* Only ring DB if ring is not empty */
> -		if (tre_ring->base && tre_ring->wp  != tre_ring->rp)
> +		if (tre_ring->base && tre_ring->wp  != tre_ring->rp &&
> +		    mhi_chan->ch_state == MHI_CH_STATE_ENABLED)
>  			mhi_ring_chan_db(mhi_cntrl, mhi_chan);
>  		read_unlock_irq(&mhi_chan->lock);
>  	}
> -- 
> 2.7.4
> 
> 

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