Import wiredtiger: cb9f737fc6c1d78a4ad50df50cdfa4047e04e6c4 from branch mongodb-4.0

ref: 1289661dc5..cb9f737fc6
for: 4.0.18

WT-5119       Birthmark records can be read as normal updates if reads race with checkpoints
WT-5376       WT_UPDATE.type field can race with visibility checks when returning key/value pairs

4 files changed, 28 insertions, 14 deletions

diff --git a/src/third_party/wiredtiger/import.data b/src/third_party/wiredtiger/import.data
index 9f5d99840e1..fede97bc1cf 100644
--- a/src/third_party/wiredtiger/import.data
+++ b/src/third_party/wiredtiger/import.data
@@ -2,5 +2,5 @@
     "vendor": "wiredtiger",
     "github": "wiredtiger/wiredtiger.git",
     "branch": "mongodb-4.0",
-    "commit": "1289661dc517fcd41326d407a04c788926db1919"
+    "commit": "cb9f737fc6c1d78a4ad50df50cdfa4047e04e6c4"
 }
diff --git a/src/third_party/wiredtiger/src/include/hardware.h b/src/third_party/wiredtiger/src/include/hardware.h
index 447d082393e..a93f1e41fbc 100644
--- a/src/third_party/wiredtiger/src/include/hardware.h
+++ b/src/third_party/wiredtiger/src/include/hardware.h
@@ -16,6 +16,13 @@
         (v) = (val);        \
     } while (0)
 
+/* Write after all previous stores are completed. */
+#define WT_ORDERED_WRITE(v, val) \
+    do {                         \
+        WT_WRITE_BARRIER();      \
+        (v) = (val);             \
+    } while (0)
+
 /*
  * Read a shared location and guarantee that subsequent reads do not see any earlier state.
  */
diff --git a/src/third_party/wiredtiger/src/include/txn.i b/src/third_party/wiredtiger/src/include/txn.i
index 38c68474397..73d953eee62 100644
--- a/src/third_party/wiredtiger/src/include/txn.i
+++ b/src/third_party/wiredtiger/src/include/txn.i
@@ -830,12 +830,17 @@ __wt_txn_read(WT_SESSION_IMPL *session, WT_UPDATE *upd, WT_UPDATE **updp)
 {
     static WT_UPDATE tombstone = {.txnid = WT_TXN_NONE, .type = WT_UPDATE_TOMBSTONE};
     WT_VISIBLE_TYPE upd_visible;
+    uint8_t type;
     bool skipped_birthmark;
 
     *updp = NULL;
+
+    type = WT_UPDATE_INVALID; /* [-Wconditional-uninitialized] */
     for (skipped_birthmark = false; upd != NULL; upd = upd->next) {
+        WT_ORDERED_READ(type, upd->type);
+
         /* Skip reserved place-holders, they're never visible. */
-        if (upd->type != WT_UPDATE_RESERVE) {
+        if (type != WT_UPDATE_RESERVE) {
             upd_visible = __wt_txn_upd_visible_type(session, upd);
             if (upd_visible == WT_VISIBLE_TRUE)
                 break;
@@ -843,14 +848,16 @@ __wt_txn_read(WT_SESSION_IMPL *session, WT_UPDATE *upd, WT_UPDATE **updp)
                 return (WT_PREPARE_CONFLICT);
         }
         /* An invisible birthmark is equivalent to a tombstone. */
-        if (upd->type == WT_UPDATE_BIRTHMARK)
+        if (type == WT_UPDATE_BIRTHMARK)
             skipped_birthmark = true;
     }
 
-    if (upd == NULL && skipped_birthmark)
+    if (upd == NULL && skipped_birthmark) {
         upd = &tombstone;
+        type = upd->type;
+    }
 
-    *updp = upd == NULL || upd->type == WT_UPDATE_BIRTHMARK ? NULL : upd;
+    *updp = upd == NULL || type == WT_UPDATE_BIRTHMARK ? NULL : upd;
     return (0);
 }
 
diff --git a/src/third_party/wiredtiger/src/reconcile/rec_visibility.c b/src/third_party/wiredtiger/src/reconcile/rec_visibility.c
index 253152e2ddd..6d881a13c05 100644
--- a/src/third_party/wiredtiger/src/reconcile/rec_visibility.c
+++ b/src/third_party/wiredtiger/src/reconcile/rec_visibility.c
@@ -87,12 +87,10 @@ __rec_append_orig_value(
     }
 
     /*
-     * If we're saving the original value for a birthmark, transfer over
-     * the transaction ID and clear out the birthmark update.
-     *
-     * Else, set the entry's transaction information to the lowest possible
-     * value. Cleared memory matches the lowest possible transaction ID and
-     * timestamp, do nothing.
+     * If we're saving the original value for a birthmark, transfer over the transaction ID and
+     * clear out the birthmark update. Else, set the entry's transaction information to the lowest
+     * possible value (as cleared memory matches the lowest possible transaction ID and timestamp,
+     * do nothing).
      */
     if (upd->type == WT_UPDATE_BIRTHMARK) {
         append->txnid = upd->txnid;
@@ -102,13 +100,15 @@ __rec_append_orig_value(
 
     /* Append the new entry into the update list. */
     WT_PUBLISH(upd->next, append);
-    __wt_cache_page_inmem_incr(session, page, size);
 
+    /* Replace the birthmark with an aborted transaction. */
     if (upd->type == WT_UPDATE_BIRTHMARK) {
-        upd->type = WT_UPDATE_STANDARD;
-        upd->txnid = WT_TXN_ABORTED;
+        WT_ORDERED_WRITE(upd->txnid, WT_TXN_ABORTED);
+        WT_ORDERED_WRITE(upd->type, WT_UPDATE_STANDARD);
     }
 
+    __wt_cache_page_inmem_incr(session, page, size);
+
 err:
     __wt_scr_free(session, &tmp);
     return (ret);