> -----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? > > > + 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 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
