Commit 93db90f7 authored by Andreas Economides's avatar Andreas Economides Committed by Tomasz Zawadzki
Browse files

nvmf/vfio-user: fix SQ race condition 



The host driver should do a wmb() before it updates the SQ tail doorbell
to ensure that any writes to the SQ are guaranteed to be visible if a
doorbell update is visible (a store-release) - and indeed, this is what
the Linux NVMe driver does.

Therefore, we require a rmb() after we read the tail doorbell in order
to synchronise properly with the host driver (we need a load-acquire),
and guarantee that the updates to the SQ are visisble to us.

Signed-off-by: default avatarAndreas Economides <andreas.economides@nutanix.com>
Change-Id: I57eb1e1f0dfb1091a8f10f40f8ee0e2604d9268c
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/9514


Community-CI: Broadcom CI <spdk-ci.pdl@broadcom.com>
Community-CI: Mellanox Build Bot
Tested-by: default avatarSPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: default avatarChangpeng Liu <changpeng.liu@intel.com>
Reviewed-by: default avatarBen Walker <benjamin.walker@intel.com>
parent 49911c47

lib/nvmf/vfio_user.c

+9 −0
Original line number Diff line number Diff line
@@ -2746,7 +2746,16 @@ nvmf_vfio_user_qpair_poll(struct nvmf_vfio_user_qpair *qpair) 


	ctrlr = qpair->ctrlr;



	/* Load-Acquire. */

	new_tail = *tdbl(ctrlr, &qpair->sq);



	/*

	 * Ensure that changes to the queue are visible to us.

	 * The host driver should write the queue first, do a wmb(), and then

	 * update the SQ tail doorbell (their Store-Release).

	 */

	spdk_rmb();



	if (sq_head(qpair) == new_tail) {

		return 0;

	}