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.
Signed-off-by: Arnd Bergmann <a...@arndb.de>
---
This is part of a longer, untested, series to remove semaphores
from the kernel, please review as such before applying.
---
lib/test_rhashtable.c | 28 ++++++++++++++++------------
1 file changed, 16 insertions(+), 12 deletions(-)
diff --git a/lib/test_rhashtable.c b/lib/test_rhashtable.c
index 18de5ff1255b..12bdea4f6c20 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
@@ -112,7 +112,8 @@ static struct rhashtable_params test_rht_params_dup = {
.automatic_shrinking = false,
};
-static struct semaphore prestart_sem, startup_sem;
+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)
@@ -635,8 +636,9 @@ 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))
+ 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]: down_interruptible failed\n", tdata->id);
for (i = 0; i < tdata->entries; i++) {
@@ -756,8 +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);
- sema_init(&startup_sem, 0);
+ atomic_set(&startup_count, tcount);
tdata = vzalloc(array_size(tcount, sizeof(struct thread_data)));
if (!tdata)
return -ENOMEM;
@@ -783,15 +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;
--
2.20.0
