RE: [PATCH v3] hv: hv_fcopy: drop the obsolete message on transfer failure

[KY Srinivasan]

> -----Original Message-----
> From: Dexuan Cui
> Sent: Tuesday, January 13, 2015 5:44 PM
> To: Vitaly Kuznetsov; KY Srinivasan
> Cc: gregkh@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; driverdev-
> devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx; apw@xxxxxxxxxxxxx;
> jasowang@xxxxxxxxxx; Haiyang Zhang
> Subject: RE: [PATCH v3] hv: hv_fcopy: drop the obsolete message on transfer
> failure
> 
> > -----Original Message-----
> > From: Vitaly Kuznetsov [mailto:vkuznets@xxxxxxxxxx]
> > Sent: Tuesday, January 13, 2015 21:52 PM
> > To: Dexuan Cui; KY Srinivasan
> > Cc: gregkh@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > driverdev- devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx;
> > apw@xxxxxxxxxxxxx; jasowang@xxxxxxxxxx; Haiyang Zhang
> > Subject: Re: [PATCH v3] hv: hv_fcopy: drop the obsolete message on
> > transfer failure
> >
> > Dexuan Cui <decui@xxxxxxxxxxxxx> writes:
> >
> > > 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.
> >
> > It seems this patch got lost and I don't see it in recent 'resend'
> > series. K.Y., Dexuan, can you please take a look?
> Hi Vitaly, Jason,
> The patch can't fix all the corner cases (it would need non-trivial efforts for
> that) as we discussed, but I think it would be better for us to have it as it can
> indeed fix an obvious issue and doesn't introduce new issues.
> 
> I think I can document the known discussed corner cases in the patch as
> TODOs and resend the patch.
> 
> Please let me know if you have different opinions. :-)

Resend the patch.

K. Y
> 
> Thanks,
> -- Dexuan
> 
> >
> > >
> > > Cc: Jason Wang <jasowang@xxxxxxxxxx>
> > > Cc: 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"
> > >
> > > v3: I added the code in fcopy_release() as Jason Wang suggested.
> > >     I removed the pr_debug (it isn't so meaningful)and added a
> > > comment
> > instead.
> > >
> > >  drivers/hv/hv_fcopy.c | 19 +++++++++++++++++++
> > >  1 file changed, 19 insertions(+)
> > >
> > > diff --git a/drivers/hv/hv_fcopy.c b/drivers/hv/hv_fcopy.c index
> > > 23b2ce2..faa6ba6 100644
> > > --- a/drivers/hv/hv_fcopy.c
> > > +++ b/drivers/hv/hv_fcopy.c
> > > @@ -86,6 +86,18 @@ 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.
> > > +	 *
> > > +	 * NOTE: fcopy_read() happens to get the semaphore (very rare)?
> We're
> > > +	 * still OK, because we've reported the failure to the host.
> > > +	 */
> > > +	if (down_trylock(&fcopy_transaction.read_sema))
> > > +		;
> > > +
> > >  }
> > >
> > >  static int fcopy_handle_handshake(u32 version) @@ -351,6 +363,13 @@
> > > static int fcopy_release(struct inode *inode, struct
> > file *f)
> > >  	 */
> > >  	in_hand_shake = true;
> > >  	opened = false;
> > > +
> > > +	if (cancel_delayed_work_sync(&fcopy_work)) {
> > > +		/* We haven't up()-ed the semaphore(very rare)? */
> > > +		if (down_trylock(&fcopy_transaction.read_sema))
> > > +			;
> > > +		fcopy_respond_to_host(HV_E_FAIL);
> > > +	}
> > >  	return 0;
> > >  }
> >
> > --
> >   Vitaly

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