From e43320ddc3a316e3410d6dde56062cf8968ea284 Mon Sep 17 00:00:00 2001

From: Nathan Hjelm <hjelmn@lanl.gov>

Date: Tue, 2 Oct 2018 15:52:45 -0600

Subject: [PATCH 38/52] btl/vader: ensure the fast box tag is always read first

On some platfoms reading a 64-bit value is non-atomic and it is

possible that the two 32-bit values are read in the wrong order. To

ensure the tag is always read first this commit reads the tag before

reading the full 64-bit value.

Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>

(cherry picked from commit 66a7dc4c72cb25df67e7f872bee7a20b5fa9c763)

---

 opal/mca/btl/vader/btl_vader_fbox.h | 12 +++++++++++-

 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/opal/mca/btl/vader/btl_vader_fbox.h b/opal/mca/btl/vader/btl_vader_fbox.h

index df1fb92..6df9a2d 100644

--- a/opal/mca/btl/vader/btl_vader_fbox.h

+++ b/opal/mca/btl/vader/btl_vader_fbox.h

@@ -56,6 +56,16 @@ static inline void mca_btl_vader_fbox_set_header (mca_btl_vader_fbox_hdr_t *hdr,

     hdr->data.tag = tag;

 }

+static inline mca_btl_vader_fbox_hdr_t mca_btl_vader_fbox_read_header (mca_btl_vader_fbox_hdr_t *hdr)

+{

+    mca_btl_vader_fbox_hdr_t tmp;

+    uint16_t tag = hdr->data.tag;

+    opal_atomic_rmb ();

+    tmp.ival = hdr->ival;

+    tmp.data.tag = tag;

+    return tmp;

+}

+

 /* attempt to reserve a contiguous segment from the remote ep */

 static inline bool mca_btl_vader_fbox_sendi (mca_btl_base_endpoint_t *ep, unsigned char tag,

                                              void * restrict header, const size_t header_size,

@@ -175,7 +185,7 @@ static inline bool mca_btl_vader_check_fboxes (void)

         int poll_count;

         for (poll_count = 0 ; poll_count <= MCA_BTL_VADER_POLL_COUNT ; ++poll_count) {

-            const mca_btl_vader_fbox_hdr_t hdr = {.ival = MCA_BTL_VADER_FBOX_HDR(ep->fbox_in.buffer + start)->ival};

+            const mca_btl_vader_fbox_hdr_t hdr = mca_btl_vader_fbox_read_header (MCA_BTL_VADER_FBOX_HDR(ep->fbox_in.buffer + start));

             /* check for a valid tag a sequence number */

             if (0 == hdr.data.tag || hdr.data.seq != ep->fbox_in.seq) {

-- 

1.8.3.1