linux-kernel - Re: [PATCH v4 4/4] bus: mhi: host: Take irqsave lock after TRE is generated

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Message-ID: <20231207063851.GD2932@thinkpad>
Date:   Thu, 7 Dec 2023 12:08:51 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Qiang Yu <quic_qianyu@...cinc.com>
Cc:     Manivannan Sadhasivam <mani@...nel.org>, quic_jhugo@...cinc.com,
        mhi@...ts.linux.dev, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, quic_cang@...cinc.com,
        quic_mrana@...cinc.com, Hemant Kumar <quic_hemantk@...cinc.com>,
        Lazarus Motha <quic_lmotha@...cinc.com>
Subject: Re: [PATCH v4 4/4] bus: mhi: host: Take irqsave lock after TRE is
 generated

On Mon, Nov 27, 2023 at 03:19:49PM +0800, Qiang Yu wrote:
> 
> On 11/24/2023 6:09 PM, Manivannan Sadhasivam wrote:
> > On Tue, Nov 14, 2023 at 01:27:41PM +0800, Qiang Yu wrote:
> > > From: Hemant Kumar <quic_hemantk@...cinc.com>
> > > 
> > > If CONFIG_TRACE_IRQFLAGS is enabled, irq will be enabled once __local_bh_
> > > enable_ip is called as part of write_unlock_bh. Hence, let's take irqsave
> > "__local_bh_enable_ip" is a function name, so you should not break it.
> Thanks for let me know, will note this in following patch.
> > 
> > > lock after TRE is generated to avoid running write_unlock_bh when irqsave
> > > lock is held.
> > > 
> > I still don't understand this commit message. Where is the write_unlock_bh()
> > being called?
> > 
> > - Mani
> Write_unlock_bh() is invoked in mhi_gen_te()
> The calling flow is like
> mhi_queue
>     read_lock_irqsave(&mhi_cntrl->pm_lock, flags)
>     mhi_gen_tre
>         write_lock_bh(&mhi_chan->lock)
>         write_unlock_bh(&mhi_chan->lock)   // Will enable irq if
> CONFIG_TRACE_IRQFLAGS is enabled
>     read_lock_irqsave(&mhi_cntrl->pm_lock, flags)
> 
> after adding this patch, the calling flow becomes
> 
> mhi_queue
>     mhi_gen_tre
>         write_lock_bh(&mhi_chan->lock)
>         write_unlock_bh(&mhi_chan->lock)
>     read_lock_irqsave(&mhi_cntrl->pm_lock, flags)
>     read_lock_irqsave(&mhi_cntrl->pm_lock, flags)

So this patch essentially fixes the issue caused by patch 1? If so, this should
be squashed into patch 1.

- Mani

> > 
> > > Signed-off-by: Hemant Kumar <quic_hemantk@...cinc.com>
> > > Signed-off-by: Lazarus Motha <quic_lmotha@...cinc.com>
> > > Signed-off-by: Qiang Yu <quic_qianyu@...cinc.com>
> > > ---
> > >   drivers/bus/mhi/host/main.c | 13 +++++--------
> > >   1 file changed, 5 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
> > > index 33f27e2..d7abd0b 100644
> > > --- a/drivers/bus/mhi/host/main.c
> > > +++ b/drivers/bus/mhi/host/main.c
> > > @@ -1128,17 +1128,15 @@ static int mhi_queue(struct mhi_device *mhi_dev, struct mhi_buf_info *buf_info,
> > >   	if (unlikely(MHI_PM_IN_ERROR_STATE(mhi_cntrl->pm_state)))
> > >   		return -EIO;
> > > -	read_lock_irqsave(&mhi_cntrl->pm_lock, flags);
> > > -
> > >   	ret = mhi_is_ring_full(mhi_cntrl, tre_ring);
> > > -	if (unlikely(ret)) {
> > > -		ret = -EAGAIN;
> > > -		goto exit_unlock;
> > > -	}
> > > +	if (unlikely(ret))
> > > +		return -EAGAIN;
> > >   	ret = mhi_gen_tre(mhi_cntrl, mhi_chan, buf_info, mflags);
> > >   	if (unlikely(ret))
> > > -		goto exit_unlock;
> > > +		return ret;
> > > +
> > > +	read_lock_irqsave(&mhi_cntrl->pm_lock, flags);
> > >   	/* Packet is queued, take a usage ref to exit M3 if necessary
> > >   	 * for host->device buffer, balanced put is done on buffer completion
> > > @@ -1158,7 +1156,6 @@ static int mhi_queue(struct mhi_device *mhi_dev, struct mhi_buf_info *buf_info,
> > >   	if (dir == DMA_FROM_DEVICE)
> > >   		mhi_cntrl->runtime_put(mhi_cntrl);
> > > -exit_unlock:
> > >   	read_unlock_irqrestore(&mhi_cntrl->pm_lock, flags);
> > >   	return ret;
> > > -- 
> > > 2.7.4
> > > 
> > > 
> 

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