> -----Original Message-----
> From: Jason Wang [mailto:jasow...@redhat.com]
> Sent: Thursday, November 27, 2014 15:15 PM
> To: Dexuan Cui
> Cc: gre...@linuxfoundation.org; linux-ker...@vger.kernel.org; driverdev-
> de...@linuxdriverproject.org; o...@aepfle.de; a...@canonical.com; KY
> Srinivasan; vkuzn...@redhat.com; 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 <vkuzn...@redhat.com>
> > Cc: K. Y. Srinivasan <k...@microsoft.com>
> > Signed-off-by: Dexuan Cui <de...@microsoft.com>
> > ---
> >
> > 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?
>
> > + 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?
Thanks,
-- Dexuan
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