linux-kernel - [PATCH tip/core/rcu 32/32] tools/memory-model: Use "-unroll 0" to keep --hw runs finite

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Date:   Wed,  2 Oct 2019 17:26:50 -0700
From:   paulmck@...nel.org
To:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        mingo@...nel.org
Cc:     stern@...land.harvard.edu, parri.andrea@...il.com, will@...nel.org,
        peterz@...radead.org, boqun.feng@...il.com, npiggin@...il.com,
        dhowells@...hat.com, j.alglave@....ac.uk, luc.maranget@...ia.fr,
        akiyks@...il.com, "Paul E. McKenney" <paulmck@...ux.ibm.com>
Subject: [PATCH tip/core/rcu 32/32] tools/memory-model: Use "-unroll 0" to keep --hw runs finite

From: "Paul E. McKenney" <paulmck@...ux.ibm.com>

Litmus tests involving atomic operations produce LL/SC loops on a number
of architectures, and unrolling these loops can result in excessive
verification times or even stack overflows.  This commit therefore uses
the "-unroll 0" herd7 argument to avoid unrolling, on the grounds that
additional passes through an LL/SC loop should not change the verification.

Note however, that certain bugs in the mapping of the LL/SC loop to
machine instructions may go undetected.  On the other hand, herd7 might
not be the best vehicle for finding such bugs in any case.  (You do
stress-test your architecture-specific code, don't you?)

Suggested-by: Luc Maranget <luc.maranget@...ia.fr>
Signed-off-by: Paul E. McKenney <paulmck@...ux.ibm.com>
---
 tools/memory-model/scripts/runlitmus.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/memory-model/scripts/runlitmus.sh b/tools/memory-model/scripts/runlitmus.sh
index dfdb1f0..94608d4b 100755
--- a/tools/memory-model/scripts/runlitmus.sh
+++ b/tools/memory-model/scripts/runlitmus.sh
@@ -75,6 +75,6 @@ then
 	cp $T/$hwlitmusfile.jingle7.out $LKMM_DESTDIR/$hwlitmus.err
 	exit 253
 fi
-/usr/bin/time $LKMM_TIMEOUT_CMD herd7 $LKMM_DESTDIR/$hwlitmus > $LKMM_DESTDIR/$hwlitmus.out 2>&1
+/usr/bin/time $LKMM_TIMEOUT_CMD herd7 -unroll 0 $LKMM_DESTDIR/$hwlitmus > $LKMM_DESTDIR/$hwlitmus.out 2>&1

 exit $?
-- 
2.9.5