linux-kernel - Re: [PATCH v2] bus: mhi: core: Check state before processing power

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Message-ID: <20210224155848.GX27945@work>
Date:   Wed, 24 Feb 2021 21:28:48 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Jeffrey Hugo <jhugo@...eaurora.org>
Cc:     hemantk@...eaurora.org, bbhatt@...eaurora.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] bus: mhi: core: Check state before processing
 power_down

On Wed, Feb 24, 2021 at 08:14:53AM -0700, Jeffrey Hugo wrote:
> On 2/24/2021 2:55 AM, Manivannan Sadhasivam wrote:
> > On Wed, Feb 17, 2021 at 09:43:31AM -0700, Jeffrey Hugo wrote:
> > > We cannot process a power_down if the power state is DISABLED.  There is
> > > no valid mhi_ctxt in that case, so attepting to process the power_down
> > > will likely result in a null pointer dereference.  If the power state is
> > > DISABLED, there is nothing to do anyways, so just bail early.
> > > 
> > > Signed-off-by: Jeffrey Hugo <jhugo@...eaurora.org>
> > > ---
> > > 
> > > v2: Fix subject and tweak the locking to avoid needless lock/unlock/relock
> > > 
> > >   drivers/bus/mhi/core/pm.c | 9 ++++++++-
> > >   1 file changed, 8 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
> > > index 56ba3ab..47f6621 100644
> > > --- a/drivers/bus/mhi/core/pm.c
> > > +++ b/drivers/bus/mhi/core/pm.c
> > > @@ -1144,6 +1144,7 @@ int mhi_async_power_up(struct mhi_controller *mhi_cntrl)
> > >   		mhi_deinit_dev_ctxt(mhi_cntrl);
> > >   error_dev_ctxt:
> > > +	mhi_cntrl->pm_state = MHI_PM_DISABLE;
> > >   	mutex_unlock(&mhi_cntrl->pm_mutex);
> > >   	return ret;
> > > @@ -1155,11 +1156,17 @@ void mhi_power_down(struct mhi_controller *mhi_cntrl, bool graceful)
> > >   	enum mhi_pm_state cur_state, transition_state;
> > >   	struct device *dev = &mhi_cntrl->mhi_dev->dev;
> > > +	mutex_lock(&mhi_cntrl->pm_mutex);
> > > +	cur_state = mhi_cntrl->pm_state;
> > 
> > As I said in my previous review, you should use pm_lock for reading the
> > pm_state.
> 
> You also said on IRC that is a refactor of the entire driver, and not a
> blocker for this fix.  Based on that, I intrepreted your comments as nothing
> needed to be done regarding the locking, so I'm confused by this comment.
> 
> I'm not entirely sure what you want since I feel like you are giving
> conflicting direction, but I'm guessing you want the lock of the pm_lock to
> be moved up to just under the mutex lock then?
> 

Yes, that's what my intention is. Sorry if I confused you.

Thanks,
Mani

> -- 
> Jeffrey Hugo
> Qualcomm Technologies, Inc. is a member of the
> Code Aurora Forum, a Linux Foundation Collaborative Project.