RE: [PATCH v2] hv: hv_fcopy: drop the obsolete message on transfer failure

[Jason Wang]

On Thu, Nov 27, 2014 at 4:50 PM, Dexuan Cui <decui@xxxxxxxxxxxxx> wrote:
> >  -----Original Message-----
> >  From: Jason Wang [mailto:jasowang@xxxxxxxxxx]
> >  Sent: Thursday, November 27, 2014 15:15 PM
> >  To: Dexuan Cui
> >  Cc: gregkh@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; 
> > driverdev-
> >  devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx; apw@xxxxxxxxxxxxx; KY
> >  Srinivasan; vkuznets@xxxxxxxxxx; Haiyang Zhang
> >  Subject: Re: [PATCH v2] hv: hv_fcopy: drop the obsolete message on 
> > transfer
> >  failure
> >  ----- Original Message -----
> >  > In the case the user-space daemon crashes, hangs or is killed, we
> >  > need to down the semaphore, otherwise, after the daemon starts 
> > next
> >  > time, the obsolete data in fcopy_transaction.message or
> >  > fcopy_transaction.fcopy_msg will be used immediately.
> >  >
> >  > Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> >  > Cc: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
> >  > Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> >  > ---
> >  >
> >  > v2: I removed the "FCP" prefix as Greg asked.
> >  >
> >  >     I also updated the output message a little:
> >  >     "FCP: failed to acquire the semaphore" -->
> >  >     "can not acquire the semaphore: it is benign"
> >  >
> >  >  drivers/hv/hv_fcopy.c | 9 +++++++++
> >  >  1 file changed, 9 insertions(+)
> >  >
> >  > diff --git a/drivers/hv/hv_fcopy.c b/drivers/hv/hv_fcopy.c
> >  > index 23b2ce2..c518ad9 100644
> >  > --- a/drivers/hv/hv_fcopy.c
> >  > +++ b/drivers/hv/hv_fcopy.c
> >  > @@ -86,6 +86,15 @@ static void fcopy_work_func(struct work_struct
> >  *dummy)
> >  >  	 * process the pending transaction.
> >  >  	 */
> >  >  	fcopy_respond_to_host(HV_E_FAIL);
> >  > +
> >  > +	/* In the case the user-space daemon crashes, hangs or is 
> > killed, we
> >  > +	 * need to down the semaphore, otherwise, after the daemon 
> > starts
> >  next
> >  > +	 * time, the obsolete data in fcopy_transaction.message or
> >  > +	 * fcopy_transaction.fcopy_msg will be used immediately.
> >  > +	 */
> >  
> >  Looks still racy, what happens if the daemon start before 
> > down_trylock()
> >  but after fcopy_respont_to_host() here?
> Jason,
> Thanks for pointing this out!
> IMO we can resolve this by adding down_trylock() in fcopy_release().
> What's your opinion?


Looks better and need to cancel the timeout also here?
> >  
> >  > +	if (down_trylock(&fcopy_transaction.read_sema))
> >  > +		pr_debug("can not acquire the semaphore: it is benign\n");
> >  
> >  typo
> >  > +
> >  >  }
> Sorry -- what typo do you mean?

s/benign/begin/ ?
> Thanks,
> -- Dexuan
> ïNrybXÇv^)Þ{.n+{zXÜ}Æz&j:+vzZ++zfh~izw?&)ßf^jÇym@Aa0hi

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