linux-kernel - [PATCH 1/4] lib/test_vmalloc.c: Replace RWSEM to SRCU for setup

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Message-Id: <20250417161216.88318-1-urezki@gmail.com>
Date: Thu, 17 Apr 2025 18:12:13 +0200
From: "Uladzislau Rezki (Sony)" <urezki@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>,
	Baoquan He <bhe@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: [PATCH 1/4] lib/test_vmalloc.c: Replace RWSEM to SRCU for setup

The test has the initialization step during which threads are
created. To prevent the workers from starting prematurely a write
lock was previously used by the main setup thread, while each
worker would block on a read lock.

Replace this RWSEM based synchronization with a simpler SRCU
based approach. Which does two basic steps:

- Main thread wraps the setup phase in an SRCU read-side
  critical section. Pair of srcu_read_lock()/srcu_read_unlock().
- Each worker calls synchronize_srcu() on entry, ensuring
  it waits for the initialization phase to be completed.

This patch eliminates the need for down_read()/up_read() and
down_write()/up_write() pairs thus simplifying the logic and
improving clarity.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
---
 lib/test_vmalloc.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/lib/test_vmalloc.c b/lib/test_vmalloc.c
index f585949ff696e..4ab23e5e772d0 100644
--- a/lib/test_vmalloc.c
+++ b/lib/test_vmalloc.c
@@ -13,9 +13,9 @@
 #include <linux/moduleparam.h>
 #include <linux/completion.h>
 #include <linux/delay.h>
-#include <linux/rwsem.h>
 #include <linux/mm.h>
 #include <linux/rcupdate.h>
+#include <linux/srcutree.h>
 #include <linux/slab.h>
 
 #define __param(type, name, init, msg)		\
@@ -58,10 +58,9 @@ __param(int, run_test_mask, INT_MAX,
 );
 
 /*
- * Read write semaphore for synchronization of setup
- * phase that is done in main thread and workers.
+ * This is for synchronization of setup phase.
  */
-static DECLARE_RWSEM(prepare_for_test_rwsem);
+DEFINE_STATIC_SRCU(prepare_for_test_srcu);
 
 /*
  * Completion tracking for worker threads.
@@ -458,7 +457,7 @@ static int test_func(void *private)
 	/*
 	 * Block until initialization is done.
 	 */
-	down_read(&prepare_for_test_rwsem);
+	synchronize_srcu(&prepare_for_test_srcu);
 
 	t->start = get_cycles();
 	for (i = 0; i < ARRAY_SIZE(test_case_array); i++) {
@@ -487,8 +486,6 @@ static int test_func(void *private)
 		t->data[index].time = delta;
 	}
 	t->stop = get_cycles();
-
-	up_read(&prepare_for_test_rwsem);
 	test_report_one_done();
 
 	/*
@@ -526,7 +523,7 @@ init_test_configuration(void)
 
 static void do_concurrent_test(void)
 {
-	int i, ret;
+	int i, ret, idx;
 
 	/*
 	 * Set some basic configurations plus sanity check.
@@ -538,7 +535,7 @@ static void do_concurrent_test(void)
 	/*
 	 * Put on hold all workers.
 	 */
-	down_write(&prepare_for_test_rwsem);
+	idx = srcu_read_lock(&prepare_for_test_srcu);
 
 	for (i = 0; i < nr_threads; i++) {
 		struct test_driver *t = &tdriver[i];
@@ -555,7 +552,7 @@ static void do_concurrent_test(void)
 	/*
 	 * Now let the workers do their job.
 	 */
-	up_write(&prepare_for_test_rwsem);
+	srcu_read_unlock(&prepare_for_test_srcu, idx);
 
 	/*
 	 * Sleep quiet until all workers are done with 1 second
-- 
2.39.5