> -----Original Message----- > From: K. Y. Srinivasan [mailto:kys@xxxxxxxxxxxxx] > Sent: Friday, March 11, 2016 12:39 PM > To: gregkh@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx; apw@xxxxxxxxxxxxx; > vkuznets@xxxxxxxxxx; jasowang@xxxxxxxxxx > Cc: KY Srinivasan <kys@xxxxxxxxxxxxx>; stable@xxxxxxxxxxxxxxx > Subject: [PATCH 1/1] Drivers: hv: vmbus: Fix a bug in > hv_need_to_signal_on_read() > > On the consumer side, we have interrupt driven flow management of the > producer. It is sufficient to base the signalling decision on the > amount of space that is available to write after the read is complete. > The current code samples the previous available space and uses this > in making the signalling decision. This state can be stale and is > unnecessary. Since the state can be stale, we end up not signalling > the host (when we should) and this can result in a hang. Fix this > problem by removing the unnecessary check. > > I would like to thank Arseney Romanenko <arseneyr@xxxxxxxxxxxxx> > for pointing out this bug. Greg, Please drop this patch. I am going to update and send the patch. K. Y > > Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx> > Tested-by: Dexuan Cui <decui@xxxxxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > --- > drivers/hv/ring_buffer.c | 7 +++---- > 1 files changed, 3 insertions(+), 4 deletions(-) > > diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c > index 5613e2b..085003a 100644 > --- a/drivers/hv/ring_buffer.c > +++ b/drivers/hv/ring_buffer.c > @@ -103,8 +103,7 @@ static bool hv_need_to_signal(u32 old_write, struct > hv_ring_buffer_info *rbi) > * there is room for the producer to send the pending packet. > */ > > -static bool hv_need_to_signal_on_read(u32 prev_write_sz, > - struct hv_ring_buffer_info *rbi) > +static bool hv_need_to_signal_on_read(struct hv_ring_buffer_info *rbi) > { > u32 cur_write_sz; > u32 r_size; > @@ -120,7 +119,7 @@ static bool hv_need_to_signal_on_read(u32 > prev_write_sz, > cur_write_sz = write_loc >= read_loc ? r_size - (write_loc - read_loc) > : > read_loc - write_loc; > > - if ((prev_write_sz < pending_sz) && (cur_write_sz >= pending_sz)) > + if (cur_write_sz >= pending_sz) > return true; > > return false; > @@ -455,7 +454,7 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info > *inring_info, > /* Update the read index */ > hv_set_next_read_location(inring_info, next_read_location); > > - *signal = hv_need_to_signal_on_read(bytes_avail_towrite, > inring_info); > + *signal = hv_need_to_signal_on_read(inring_info); > > return ret; > } > -- > 1.7.4.1 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
