linux-kernel - Re: [PATCH 5.10 002/299] bus: mhi: core: Clear configuration from channel context during reset

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Date:   Tue, 11 May 2021 11:47:28 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Pavel Machek <pavel@...x.de>, bbhatt@...eaurora.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Hemant Kumar <hemantk@...eaurora.org>
Subject: Re: [PATCH 5.10 002/299] bus: mhi: core: Clear configuration from
 channel context during reset

Hi Pavel,

On Mon, May 10, 2021 at 10:56:50PM +0200, Pavel Machek wrote:
> Hi!
> 
> > From: Bhaumik Bhatt <bbhatt@...eaurora.org>
> > 
> > commit 47705c08465931923e2f2b506986ca0bdf80380d upstream.
> > 
> > When clearing up the channel context after client drivers are
> > done using channels, the configuration is currently not being
> > reset entirely. Ensure this is done to appropriately handle
> > issues where clients unaware of the context state end up calling
> > functions which expect a context.
> 
> > +++ b/drivers/bus/mhi/core/init.c
> > @@ -544,6 +544,7 @@ void mhi_deinit_chan_ctxt(struct mhi_con
> > +	u32 tmp;
> > @@ -554,7 +555,19 @@ void mhi_deinit_chan_ctxt(struct mhi_con
> ...
> > +	tmp = chan_ctxt->chcfg;
> > +	tmp &= ~CHAN_CTX_CHSTATE_MASK;
> > +	tmp |= (MHI_CH_STATE_DISABLED << CHAN_CTX_CHSTATE_SHIFT);
> > +	chan_ctxt->chcfg = tmp;
> > +
> > +	/* Update to all cores */
> > +	smp_wmb();
> >  }
> 
> This is really interesting code; author was careful to make sure chcfg
> is updated atomically, but C compiler is free to undo that. Plus, this
> will make all kinds of checkers angry.
> 
> Does the file need to use READ_ONCE and WRITE_ONCE?
> 

Thanks for looking into this.

I agree that the order could be mangled between chcfg read & write and
using READ_ONCE & WRITE_ONCE seems to be a good option.

Bhaumik, can you please submit a patch and tag stable?

Thanks,
Mani

> Best regards,
> 								Pavel
> -- 
> DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany