Public bug reported:
Fix bugs in signaling the Hyper-V host when freeing space in the
host->guest ring buffer:
1. The interrupt_mask must not be used to determine whether to signal
on the host->guest ring buffer
2. The ring buffer write_index must be read (via hv_get_bytes_to_write)
*after* pending_send_sz is read in order to avoid a race condition
3. Comparisons with pending_send_sz must treat the "equals" case as
not-enough-space
4. Don't signal if the pending_send_sz feature is not present. Older
versions of Hyper-V that don't implement this feature will poll.
Fixes: 03bad714a161 ("vmbus: more host signalling avoidance")
This patch is on its way upstream but has not yet been accepted into
char-misc. It should apply to 4.4+ kernels that have taken 03bad714a161
** Affects: linux-azure (Ubuntu)
Importance: Undecided
Status: New
** Patch added: "Drivers: hv: vmbus: Fix ring buffer signaling patch"
https://bugs.launchpad.net/bugs/1748662/+attachment/5052734/+files/0001-Drivers-hv-vmbus-Fix-ring-buffer-signaling.patch
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https://bugs.launchpad.net/bugs/1748662
Title:
[Hyper-V] Drivers: hv: vmbus: Fix ring buffer signaling
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