> -----Original Message-----
> From: K. Y. Srinivasan [mailto:k...@microsoft.com]
> Sent: Friday, March 11, 2016 12:39 PM
> To: gre...@linuxfoundation.org; linux-ker...@vger.kernel.org;
> de...@linuxdriverproject.org; o...@aepfle.de; a...@canonical.com;
> vkuzn...@redhat.com; jasow...@redhat.com
> Cc: KY Srinivasan <k...@microsoft.com>; sta...@vger.kernel.org
> 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 <arsen...@microsoft.com>
> 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 <k...@microsoft.com>
> Tested-by: Dexuan Cui <de...@microsoft.com>
> Cc: <sta...@vger.kernel.org>
> ---
> 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
de...@linuxdriverproject.org
http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
