Messages in this thread | | | Date | Thu, 5 Aug 2010 07:19:29 +0200 | From | Vitezslav Samel <> | Subject | Re: [PATCHv3 03/16] pps: fix race in PPS_FETCH handler |
| |
On Thu, Aug 05, 2010 at 01:06:40AM +0400, Alexander Gordeev wrote: > There was a race in PPS_FETCH ioctl handler when several processes want > to obtain PPS data simultaneously using sleeping PPS_FETCH. They all > sleep most of the time in the system call. > With the old approach when the first process waiting on the pps queue > is waken up it makes new system call right away and zeroes pps->go. So > other processes continue to sleep. This is a clear race condition > because of the global 'go' variable. > With the new approach pps->last_ev holds some value increasing at each > PPS event. PPS_FETCH ioctl handler saves current value to the local > variable at the very beginning so it can safely check that there is a > new event by just comparing both variables. > > Signed-off-by: Alexander Gordeev <lasaine@lvk.cs.msu.su> > --- > drivers/pps/kapi.c | 4 ++-- > drivers/pps/pps.c | 10 +++++++--- > include/linux/pps_kernel.h | 2 +- > 3 files changed, 10 insertions(+), 6 deletions(-) > > diff --git a/drivers/pps/kapi.c b/drivers/pps/kapi.c > index 55f3961..3f89f5e 100644 > --- a/drivers/pps/kapi.c > +++ b/drivers/pps/kapi.c > @@ -326,8 +326,8 @@ void pps_event(int source, struct pps_ktime *ts, int event, void *data) > > /* Wake up if captured something */ > if (captured) { > - pps->go = ~0; > - wake_up_interruptible(&pps->queue); > + pps->last_ev++; > + wake_up_interruptible_all(&pps->queue);
What happens if pps->last_ev overflows? Seems to me it would freeze pps.
Cheers, Vita
| |