tcwg_kernel-bisect.sh: Fix re-triggering bisection with invalid range

When re-triggering bisections due to bad $last_good commit, we
need to check that baseline_rev is a parent of last_good -- otherwise
we will end up with invalid bisection interval.

Change-Id: Ic9f9e07783c967f2aef777105a26f02e526a8505

1 files changed, 23 insertions, 12 deletions

diff --git a/tcwg_kernel-bisect.sh b/tcwg_kernel-bisect.sh
index 468b4bc6..12d48f68 100755
--- a/tcwg_kernel-bisect.sh
+++ b/tcwg_kernel-bisect.sh
@@ -289,6 +289,8 @@ fi
 
 first_bad=$(get_first_bad)
 if [ x"$first_bad" != x"" ]; then
+    # "git bisect run" succeeded.  Check whether this is an actual regression
+    # or bisection artifact.
     res=0
     for last_good in $last_good $(git rev-parse $first_bad^@); do
 	# It seems that git-bisect assumes parent commit as "good" on
@@ -307,29 +309,38 @@ if [ x"$first_bad" != x"" ]; then
 	    break
 	fi
     done
-    if [ x"$res" != x"0" ]; then
+    if [ x"$res" = x"0" ]; then
+	# Success!
+	push_interesting_commits $first_bad $last_good
+	# Touch $artifacts/first-bad as a marker of successful bisect.
+	echo $first_bad > $artifacts/first-bad
+    else
 	# It seems $last_good was on a path that tested good, even though
 	# it itself is bad.  We re-trigger the bisection job with updated
 	# parameters.
+	push_interesting_commits $last_good
+
 	# We need to be careful to avoid re-trigger loops, so verify that
 	# last_good is an ancestor of bad_rev.
 	assert git merge-base --is-ancestor $last_good $bad_rev
-	cat > $artifacts/trigger-bisect <<EOF
+	if git merge-base --is-ancestor $baseline_rev $last_good; then
+	    # $last_good is a child of $baseline_rev, so we can re-trigger
+	    # bisection with reduced bisection range.
+	    cat > $artifacts/trigger-bisect <<EOF
 current_project=$current_project
 baseline_branch=$baseline_rev
 bad_branch=$last_good
 EOF
-	# Don't send any emails.
-	echo > $artifacts/jenkins/mail-recipients.txt
-	touch $artifacts/jenkins/build-name
-	sed -i -e "s/\$/-last_good-bad/" $artifacts/jenkins/build-name
-	push_interesting_commits $last_good
-	trap "" EXIT
-	exit 0
+	    touch $artifacts/jenkins/build-name
+	    sed -i -e "s/\$/-last_good-bad/" $artifacts/jenkins/build-name
+	    # Don't send any emails.
+	    echo > $artifacts/jenkins/mail-recipients.txt
+	    trap "" EXIT
+	    exit 0
+	fi
+	# This case will be handled similar to "git bisect run" failure below.
+	# We are going to reset baseline to $first_bad.
     fi
-
-    push_interesting_commits $first_bad $last_good
-    echo $first_bad > $artifacts/first-bad
 else
     # When "git bisect run" fails, e.g., due to merge-base of $baseline_rev and
     # $bad_rev is worse than $baseline_rev, we want to reset baseline to HEAD,