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.

[urezki@gmail.com: fix compile error with CONFIG_TINY_RCU]
Link: https://lkml.kernel.org/r/20250420142029.103169-1-urezki@gmail.com
Link: https://lkml.kernel.org/r/20250417161216.88318-1-urezki@gmail.com
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Adrian Huang <ahuang12@lenovo.com>
Tested-by: Adrian Huang <ahuang12@lenovo.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Christop Hellwig <hch@infradead.org>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/lib/test_vmalloc.c b/lib/test_vmalloc.c
index f585949ff696eec107d485d03d64f5267d54b313..399751022eead73cd68b8a8109134e1a3e0d3eb1 100644 (file)
--- 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/srcu.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