Add basic spinlock tests to regression tests.

As s_lock_test, the already existing test for spinlocks, isn't run in
an automated fashion (and doesn't test a normal backend environment),
adding tests that are run as part of a normal regression run is a good
idea. Particularly in light of several recent and upcoming spinlock
related fixes.

Currently the new tests are run as part of the pre-existing
test_atomic_ops() test. That perhaps can be quibbled about, but for
now seems ok.

The only operations that s_lock_test tests but the new tests don't are
the detection of a stuck spinlock and S_LOCK_FREE (which is otherwise
unused, not implemented on all platforms, and will be removed).

This currently contains a test for more than INT_MAX spinlocks (only
run with --disable-spinlocks), to ensure the recent commit fixing a
bug with more than INT_MAX spinlock initializations is correct. That
test is somewhat slow, so we might want to disable it after a few
days.

It might be worth retiring s_lock_test after this. The added coverage
of a stuck spinlock probably isn't worth the added complexity?

Author: Andres Freund
Discussion: https://postgr.es/m/20200606023103.avzrctgv7476xj7i@alap3.anarazel.de

diff --git a/src/test/regress/regress.c b/src/test/regress/regress.c
index 960c155e5f23882bfed962d4bfb8089500f43c1e..9bea2ada24aab47b6fe9c0c40b7968d2a639ffa9 100644 (file)
--- a/src/test/regress/regress.c
+++ b/src/test/regress/regress.c
@@ -34,6 +34,7 @@
 #include "optimizer/optimizer.h"
 #include "optimizer/plancat.h"
 #include "port/atomics.h"
+#include "storage/spin.h"
 #include "utils/builtins.h"
 #include "utils/geo_decls.h"
 #include "utils/memutils.h"
@@ -794,6 +795,108 @@ test_atomic_uint64(void)
    EXPECT_EQ_U64(pg_atomic_fetch_and_u64(&var, ~0), 0);
 }
 
+/*
+ * Perform, fairly minimal, testing of the spinlock implementation.
+ *
+ * It's likely worth expanding these to actually test concurrency etc, but
+ * having some regularly run tests is better than none.
+ */
+static void
+test_spinlock(void)
+{
+   /*
+    * Basic tests for spinlocks, as well as the underlying operations.
+    *
+    * We embed the spinlock in a struct with other members to test that the
+    * spinlock operations don't perform too wide writes.
+    */
+   {
+       struct test_lock_struct
+       {
+           char        data_before[4];
+           slock_t     lock;
+           char        data_after[4];
+       } struct_w_lock;
+
+       memcpy(struct_w_lock.data_before, "abcd", 4);
+       memcpy(struct_w_lock.data_after, "ef12", 4);
+
+       /* test basic operations via the SpinLock* API */
+       SpinLockInit(&struct_w_lock.lock);
+       SpinLockAcquire(&struct_w_lock.lock);
+       SpinLockRelease(&struct_w_lock.lock);
+
+       /* test basic operations via underlying S_* API */
+       S_INIT_LOCK(&struct_w_lock.lock);
+       S_LOCK(&struct_w_lock.lock);
+       S_UNLOCK(&struct_w_lock.lock);
+
+       /* and that "contended" acquisition works */
+       s_lock(&struct_w_lock.lock, "testfile", 17, "testfunc");
+       S_UNLOCK(&struct_w_lock.lock);
+
+       /*
+        * Check, using TAS directly, that a single spin cycle doesn't block
+        * when acquiring an already acquired lock.
+        */
+#ifdef TAS
+       S_LOCK(&struct_w_lock.lock);
+
+       if (!TAS(&struct_w_lock.lock))
+           elog(ERROR, "acquired already held spinlock");
+
+#ifdef TAS_SPIN
+       if (!TAS_SPIN(&struct_w_lock.lock))
+           elog(ERROR, "acquired already held spinlock");
+#endif                         /* defined(TAS_SPIN) */
+
+       S_UNLOCK(&struct_w_lock.lock);
+#endif                         /* defined(TAS) */
+
+       /*
+        * Verify that after all of this the non-lock contents are still
+        * correct.
+        */
+       if (memcmp(struct_w_lock.data_before, "abcd", 4) != 0)
+           elog(ERROR, "padding before spinlock modified");
+       if (memcmp(struct_w_lock.data_after, "ef12", 4) != 0)
+           elog(ERROR, "padding after spinlock modified");
+   }
+
+   /*
+    * Ensure that allocating more than INT32_MAX emulated spinlocks
+    * works. That's interesting because the spinlock emulation uses a 32bit
+    * integer to map spinlocks onto semaphores. There've been bugs...
+    */
+#ifndef HAVE_SPINLOCKS
+   {
+       /*
+        * Initialize enough spinlocks to advance counter close to
+        * wraparound. It's too expensive to perform acquire/release for each,
+        * as those may be syscalls when the spinlock emulation is used (and
+        * even just atomic TAS would be expensive).
+        */
+       for (uint32 i = 0; i < INT32_MAX - 100000; i++)
+       {
+           slock_t lock;
+
+           SpinLockInit(&lock);
+       }
+
+       for (uint32 i = 0; i < 200000; i++)
+       {
+           slock_t lock;
+
+           SpinLockInit(&lock);
+
+           SpinLockAcquire(&lock);
+           SpinLockRelease(&lock);
+           SpinLockAcquire(&lock);
+           SpinLockRelease(&lock);
+       }
+   }
+#endif
+}
 
 PG_FUNCTION_INFO_V1(test_atomic_ops);
 Datum
@@ -805,6 +908,12 @@ test_atomic_ops(PG_FUNCTION_ARGS)
 
    test_atomic_uint64();
 
+   /*
+    * Arguably this shouldn't be tested as part of this function, but it's
+    * closely enough related that that seems ok for now.
+    */
+   test_spinlock();
+
    PG_RETURN_BOOL(true);
 }