Re: [PATCH v3 1/1] bus: mhi: host: Fix up null pointer access in mhi_irq_handler

From: Manivannan Sadhasivam <mani@kernel.org>
To: Kalle Valo <kvalo@kernel.org>
Cc: Qiang Yu <quic_qianyu@quicinc.com>,
	quic_hemantk@quicinc.com, loic.poulain@linaro.org,
	quic_jhugo@quicinc.com, mhi@lists.linux.dev,
	linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
	quic_cang@quicinc.com, ath11k@lists.infradead.org
Subject: Re: [PATCH v3 1/1] bus: mhi: host: Fix up null pointer access in mhi_irq_handler
Date: Fri, 29 Jul 2022 19:52:21 +0530	[thread overview]
Message-ID: <20220729142221.GA9937@thinkpad> (raw)
In-Reply-To: <87czdrrc95.fsf@kernel.org>

On Tue, Jul 26, 2022 at 08:53:58PM +0300, Kalle Valo wrote:
> Manivannan Sadhasivam <mani@kernel.org> writes:
> 
> > +ath11k, Kalle
> >
> > On Fri, Jul 22, 2022 at 11:17:18AM +0800, Qiang Yu wrote:
> >> The irq handler for a shared IRQ ought to be prepared for running
> >> even now it's being freed. So let's check the pointer used by
> >> mhi_irq_handler to avoid null pointer access since it is probably
> >> released before freeing IRQ.
> >> 
> >> Signed-off-by: Qiang Yu <quic_qianyu@quicinc.com>
> >
> > Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
> 
> This fixes the crash and my regression tests pass now, thanks. But
> please see my question below.
> 
> Tested-by: Kalle Valo <kvalo@kernel.org>
> 

Thanks Kalle!

> >> +	/*
> >> +	 * If CONFIG_DEBUG_SHIRQ is set, the IRQ handler will get invoked during __free_irq()
> >> +	 * and by that time mhi_ctxt() would've freed. So check for the existence of mhi_ctxt
> >> +	 * before handling the IRQs.
> >> +	 */
> >> +	if (!mhi_cntrl->mhi_ctxt) {
> >> +		dev_dbg(&mhi_cntrl->mhi_dev->dev,
> >> +			"mhi_ctxt has been freed\n");
> >> +		return IRQ_HANDLED;
> >> +	}
> 
> I don't see any protection accessing mhi_cntrl->mhi_ctxt, is this really
> free of race conditions?
> 

As Qiang said, it is safe to access mhi_ctxt here.

Thanks,
Mani

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