Re: [PATCH v2] bus: mhi: core: Check state before processing power_down

[Jeffrey Hugo]

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@xxxxxxxxxxxxxx>
> > ---
> >
> > 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?

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