linux-kernel - Re: [Linaro-acpi] [PATCH] Mailbox: Complete wait event only if Tx was successful

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Message-ID: <20141216113602.GA21888@e103737-lin.cambridge.arm.com>
Date:	Tue, 16 Dec 2014 11:36:02 +0000
From:	Sudeep Holla <sudeep.holla@....com>
To:	Ashwin Chaugule <ashwin.chaugule@...aro.org>
Cc:	"jaswinder.singh@...aro.org" <jaswinder.singh@...aro.org>,
	"arnd@...db.de" <arnd@...db.de>,
	"patches@...aro.org" <patches@...aro.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"broonie@...nel.org" <broonie@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Sudeep Holla <sudeep.holla@....com>
Subject: Re: [Linaro-acpi] [PATCH] Mailbox: Complete wait event only if Tx
 was successful

On Fri, Dec 12, 2014 at 05:47:26PM +0000, Ashwin Chaugule wrote:
> On 12 December 2014 at 03:43, Sudeep Holla <sudeep.holla@....com> wrote:
> > Hi Ashwin,
> 
> Hi,
>

Hi Ashwin,

> > On Thursday 11 December 2014 01:46 AM, Ashwin Chaugule wrote:
> >>
> >> If a wait_for_completion_timeout() call returns due to a timeout,
> >> the mbox code can still call complete() after returning from the wait.
> >> This can cause subsequent transmissions on a channel to fail, since
> >> the wait_for_completion_timeout() sees the completion variable
> >> is !=0, caused by the erroneous complete() call, and immediately
> >> returns without waiting for the time as expected by the client.
> >>
> >> Fix this by calling complete() only if the TX was successful.
> >>
> >> Signed-off-by: Ashwin Chaugule <ashwin.chaugule@...aro.org>
> >> ---
> >>   drivers/mailbox/mailbox.c | 2 +-
> >>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
> >> index 17e9e4a..4acaddb 100644
> >> --- a/drivers/mailbox/mailbox.c
> >> +++ b/drivers/mailbox/mailbox.c
> >> @@ -101,7 +101,7 @@ static void tx_tick(struct mbox_chan *chan, int r)
> >>         if (mssg && chan->cl->tx_done)
> >>                 chan->cl->tx_done(chan->cl, mssg, r);
> >>
> >> -       if (chan->cl->tx_block)
> >> +       if ((!r) && chan->cl->tx_block)
> >>                 complete(&chan->tx_complete);
> >
> >
> > Just curious to check if there's another possible race which is
> > a different issue.
> >
> > Suppose the timer fired and indicated that the Tx is complete, then
> > it tries to execute complete while the wait_for_completion_timeout timed
> > out. Does that make sense ?
> >
> > So if yes, how about adding !completion_done(..) to the check while you
> > are at this ?
> 
> Yea. Seems like another race condition. I'll add it along with this..
> 

Thanks !

Regards,
Sudeep

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