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

[Adrian Huang12]

> -----Original Message-----
> From: owner-linux-mm@xxxxxxxxx <owner-linux-mm@xxxxxxxxx> On Behalf
> Of Uladzislau Rezki (Sony)
> Sent: Friday, April 18, 2025 12:12 AM
> To: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx; LKML <linux-kernel@xxxxxxxxxxxxxxx>; Baoquan He
> <bhe@xxxxxxxxxx>; Christoph Hellwig <hch@xxxxxxxxxxxxx>; Uladzislau Rezki
> <urezki@xxxxxxxxx>; Oleksiy Avramchenko <oleksiy.avramchenko@xxxxxxxx>
> Subject: [External] [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@xxxxxxxxx>
> ---
>  lib/test_vmalloc.c | 17 +++++++----------
>  1 file changed, 7 insertions(+), 10 deletions(-)

Reviewed-by: Adrian Huang <ahuang12@xxxxxxxxxx>
Tested-by: Adrian Huang <ahuang12@xxxxxxxxxx>

> 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
>