test_rhashtable: remove semaphore usage

This is one of only two files that initialize a semaphore to a negative
value. We don't really need the two semaphores here at all, but can do
the same thing in more conventional and more effient way, by using a
single waitqueue and an atomic thread counter.

This gets us a little bit closer to eliminating classic semaphores from
the kernel. It also fixes a corner case where we fail to continue after
one of the threads fails to start up.

An alternative would be to use a split kthread_create()+wake_up_process()
and completely eliminate the separate synchronization.

Acked-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 19 insertions, 13 deletions

diff --git a/lib/test_rhashtable.c b/lib/test_rhashtable.c
index 82ac39ce5310..6a8ac7626797 100644
--- a/lib/test_rhashtable.c
+++ b/lib/test_rhashtable.c
@@ -20,11 +20,11 @@
 #include <linux/module.h>
 #include <linux/rcupdate.h>
 #include <linux/rhashtable.h>
-#include <linux/semaphore.h>
 #include <linux/slab.h>
 #include <linux/sched.h>
 #include <linux/random.h>
 #include <linux/vmalloc.h>
+#include <linux/wait.h>
 
 #define MAX_ENTRIES     1000000
 #define TEST_INSERT_FAIL INT_MAX
@@ -112,8 +112,8 @@ static struct rhashtable_params test_rht_params_dup = {
         .automatic_shrinking = false,
 };
 
-static struct semaphore prestart_sem;
-static struct semaphore startup_sem = __SEMAPHORE_INITIALIZER(startup_sem, 0);
+static atomic_t startup_count;
+static DECLARE_WAIT_QUEUE_HEAD(startup_wait);
 
 static int insert_retry(struct rhashtable *ht, struct test_obj *obj,
                         const struct rhashtable_params params)
@@ -634,9 +634,12 @@ static int threadfunc(void *data)
         int i, step, err = 0, insert_retries = 0;
         struct thread_data *tdata = data;
 
-        up(&prestart_sem);
-        if (down_interruptible(&startup_sem))
-                pr_err("  thread[%d]: down_interruptible failed\n", tdata->id);
+        if (atomic_dec_and_test(&startup_count))
+                wake_up(&startup_wait);
+        if (wait_event_interruptible(startup_wait, atomic_read(&startup_count) == -1)) {
+                pr_err("  thread[%d]: interrupted\n", tdata->id);
+                goto out;
+        }
 
         for (i = 0; i < tdata->entries; i++) {
                 tdata->objs[i].value.id = i;
@@ -755,7 +758,7 @@ static int __init test_rht_init(void)
 
         pr_info("Testing concurrent rhashtable access from %d threads\n",
                 tcount);
-        sema_init(&prestart_sem, 1 - tcount);
+        atomic_set(&startup_count, tcount);
         tdata = vzalloc(array_size(tcount, sizeof(struct thread_data)));
         if (!tdata)
                 return -ENOMEM;
@@ -781,15 +784,18 @@ static int __init test_rht_init(void)
                 tdata[i].objs = objs + i * entries;
                 tdata[i].task = kthread_run(threadfunc, &tdata[i],
                                             "rhashtable_thrad[%d]", i);
-                if (IS_ERR(tdata[i].task))
+                if (IS_ERR(tdata[i].task)) {
                         pr_err(" kthread_run failed for thread %d\n", i);
-                else
+                        atomic_dec(&startup_count);
+                } else {
                         started_threads++;
+                }
         }
-        if (down_interruptible(&prestart_sem))
-                pr_err("  down interruptible failed\n");
-        for (i = 0; i < tcount; i++)
-                up(&startup_sem);
+        if (wait_event_interruptible(startup_wait, atomic_read(&startup_count) == 0))
+                pr_err("  wait_event interruptible failed\n");
+        /* count is 0 now, set it to -1 and wake up all threads together */
+        atomic_dec(&startup_count);
+        wake_up_all(&startup_wait);
         for (i = 0; i < tcount; i++) {
                 if (IS_ERR(tdata[i].task))
                         continue;