Re: [PATCH v2 1/2] bus: mhi: host: Add spinlock to protect WP access when queueing TREs

[Qiang Yu]

On 11/6/2023 12:41 PM, Manivannan Sadhasivam wrote:
> On Wed, Sep 13, 2023 at 04:47:40PM +0800, Qiang Yu wrote:
> > From: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
> >
> > Protect WP accesses such that multiple threads queueing buffers for
> > incoming data do not race and access the same WP twice. Ensure read and
> > write locks for the channel are not taken in succession by dropping the
> > read lock from parse_xfer_event() such that a callback given to client
> > can potentially queue buffers and acquire the write lock in that process.
> > Any queueing of buffers should be done without channel read lock acquired
> > as it can result in multiple locks and a soft lockup.
> This change is doing two things:
>
> 1. Unlocking xfer_cb to prevent potential lockup
> 2. Protecting mhi_gen_tre() against concurrent access
>
> So you should split this into two patches and also add Fixes tag if appropriate.
>
> - Mani
Hi Mani, thanks for review. I split this into two patch and add Fixes tag.
> > Signed-off-by: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
> > Signed-off-by: Qiang Yu <quic_qianyu@xxxxxxxxxxx>
> > ---
> >   drivers/bus/mhi/host/main.c | 11 ++++++++++-
> >   1 file changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
> > index dcf627b..13c4b89 100644
> > --- a/drivers/bus/mhi/host/main.c
> > +++ b/drivers/bus/mhi/host/main.c
> > @@ -642,6 +642,7 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl,
> >   			mhi_del_ring_element(mhi_cntrl, tre_ring);
> >   			local_rp = tre_ring->rp;
> >   
> > +			read_unlock_bh(&mhi_chan->lock);
> >   			/* notify client */
> >   			mhi_chan->xfer_cb(mhi_chan->mhi_dev, &result);
> >   
> > @@ -667,6 +668,7 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl,
> >   					kfree(buf_info->cb_buf);
> >   				}
> >   			}
> > +			read_lock_bh(&mhi_chan->lock);
> >   		}
> >   		break;
> >   	} /* CC_EOT */
> > @@ -1204,6 +1206,9 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
> >   	int eot, eob, chain, bei;
> >   	int ret;
> >   
> > +	/* Protect accesses for reading and incrementing WP */
> > +	write_lock_bh(&mhi_chan->lock);
> > +
> >   	buf_ring = &mhi_chan->buf_ring;
> >   	tre_ring = &mhi_chan->tre_ring;
> >   
> > @@ -1221,8 +1226,10 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
> >   
> >   	if (!info->pre_mapped) {
> >   		ret = mhi_cntrl->map_single(mhi_cntrl, buf_info);
> > -		if (ret)
> > +		if (ret) {
> > +			write_unlock_bh(&mhi_chan->lock);
> >   			return ret;
> > +		}
> >   	}
> >   
> >   	eob = !!(flags & MHI_EOB);
> > @@ -1239,6 +1246,8 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
> >   	mhi_add_ring_element(mhi_cntrl, tre_ring);
> >   	mhi_add_ring_element(mhi_cntrl, buf_ring);
> >   
> > +	write_unlock_bh(&mhi_chan->lock);
> > +
> >   	return 0;
> >   }
> >   
> > --
> > 2.7.4