test: fix race in transition/maps008 that lead to fail of test

Running test/zdtm.py run -t zdtm/transition/maps008 --snap --pre 30
in a loop I got test failure with "Mem differs"
error each ~20 minutes. The cause of the bug is in lack of
synchronization between processes that still do datagen stage of
test and processes that already do datacheck stage of test.
As a result we can get "Mem differs" error if:
1. Process P1 being on datacheck stage fetches a byte with
   offset X from ashmem vma VMA1 into CPU register.
2. Process P2 still being on datagen stage changes byte with offset X
   in the same ashmem vma VMA1.
3. Process P1 fetches byte with offset X from another ashmem vma VMA2
   mapped to the same physical memory as VMA1.
4. Process P1 compares two fetched bytes and finds out that they
   have different values.
5. Process P1 reports "Mem differs" error.

Race is fixed by waiting for all processes to exit datagen stage
before proceeding to datacheck stage.
Signed-off-by: Eugene Batalov <eabatalov89@gmail.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

test/zdtm/transition/maps008.c

@@ -12,6 +12,7 @@
 #include <sys/wait.h>
 #include <linux/limits.h>
 #include "zdtmtst.h"
+#include "lock.h"
 
 const char *test_doc = "ps tree with anon shared vmas for dedup";
 
@@ -134,6 +135,7 @@ static void chk_proc_mem_eq(pid_t pid1, void *addr1, unsigned long size1,
  * |       |          |
  * proc111 proc112    proc131
  */
+#define PROC_CNT 7
 
 #define PROC1_PGIX 0
 #define PROC11_PGIX 1
@@ -157,6 +159,12 @@ struct pstree {
 };
 struct pstree *pstree;
 
+struct test_sync {
+	futex_t datagen;
+	futex_t datagen_exit_cnt;
+};
+struct test_sync *test_sync;
+
 size_t mem1_size = 1L << 20;
 size_t mem2_size = 1L << 21;
 size_t mem3_size = 1L << 22;
@@ -180,7 +188,7 @@ void datagen_each_pg(uint8_t *mem, size_t size, size_t off, uint32_t crc_epoch)
 	if (!mem)
 		return;
 
-	while (test_go() && (off < size)) {
+	while (futex_get(&test_sync->datagen) && (off < size)) {
 		uint32_t crc = crc_epoch;
 
 		datagen(mem + off, CRC_EPOCH_OFFSET, &crc);
@@ -239,8 +247,9 @@ static int proc131_func(task_waiter_t *setup_waiter)
 	mems_datagen_each_pgix(PROC131_PGIX, &crc_epoch);
 	task_waiter_complete_current(setup_waiter);
 
-	while (test_go())
+	while (futex_get(&test_sync->datagen))
 		mems_datagen_each_pgix(PROC131_PGIX, &crc_epoch);
+	futex_inc_and_wake(&test_sync->datagen_exit_cnt);
 	test_waitsig();
 
 	mems_datachck_each_pgix(PROC131_PGIX);
@@ -265,8 +274,9 @@ static int proc13_func(task_waiter_t *setup_waiter)
 	fork_and_setup(proc131_func);
 	task_waiter_complete_current(setup_waiter);
 
-	while (test_go())
+	while (futex_get(&test_sync->datagen))
 		mems_datagen_each_pgix(PROC13_PGIX, &crc_epoch);
+	futex_inc_and_wake(&test_sync->datagen_exit_cnt);
 	test_waitsig();
 
 	mems_datachck_each_pgix(PROC13_PGIX);
@@ -290,8 +300,9 @@ static int proc12_func(task_waiter_t *setup_waiter)
 	mems_datagen_each_pgix(PROC12_PGIX, &crc_epoch);
 	task_waiter_complete_current(setup_waiter);
 
-	while (test_go())
+	while (futex_get(&test_sync->datagen))
 		mems_datagen_each_pgix(PROC12_PGIX, &crc_epoch);
+	futex_inc_and_wake(&test_sync->datagen_exit_cnt);
 	test_waitsig();
 
 	mems_datachck_each_pgix(PROC12_PGIX);
@@ -307,8 +318,9 @@ static int proc111_func(task_waiter_t *setup_waiter)
 	mems_datagen_each_pgix(PROC111_PGIX, &crc_epoch);
 	task_waiter_complete_current(setup_waiter);
 
-	while (test_go())
+	while (futex_get(&test_sync->datagen))
 		mems_datagen_each_pgix(PROC111_PGIX, &crc_epoch);
+	futex_inc_and_wake(&test_sync->datagen_exit_cnt);
 	test_waitsig();
 
 	mems_datachck_each_pgix(PROC111_PGIX);
@@ -323,8 +335,9 @@ static int proc112_func(task_waiter_t *setup_waiter)
 	mems_datagen_each_pgix(PROC112_PGIX, &crc_epoch);
 	task_waiter_complete_current(setup_waiter);
 
-	while (test_go())
+	while (futex_get(&test_sync->datagen))
 		mems_datagen_each_pgix(PROC112_PGIX, &crc_epoch);
+	futex_inc_and_wake(&test_sync->datagen_exit_cnt);
 	test_waitsig();
 
 	mems_datachck_each_pgix(PROC112_PGIX);
@@ -350,8 +363,9 @@ static int proc11_func(task_waiter_t *setup_waiter)
 	mems_datagen_each_pgix(PROC11_PGIX, &crc_epoch);
 	task_waiter_complete_current(setup_waiter);
 
-	while (test_go())
+	while (futex_get(&test_sync->datagen))
 		mems_datagen_each_pgix(PROC11_PGIX, &crc_epoch);
+	futex_inc_and_wake(&test_sync->datagen_exit_cnt);
 	test_waitsig();
 
 	mems_datachck_each_pgix(PROC11_PGIX);
@@ -386,6 +400,7 @@ static int proc1_func(void)
 	uint32_t crc_epoch = 0;
 	uint8_t *mem2_old = NULL;
 
+	futex_set(&test_sync->datagen, 1);
 	pstree->proc1 = getpid();
 	mem1 = mmap_ashmem(mem1_size);
 	mem2 = mmap_ashmem(mem2_size);
@@ -410,6 +425,9 @@ static int proc1_func(void)
 	while (test_go())
 		mems_datagen_each_pgix(PROC1_PGIX, &crc_epoch);
 	test_waitsig();
+	futex_set(&test_sync->datagen_exit_cnt, 0);
+	futex_set(&test_sync->datagen, 0);
+	futex_wait_while(&test_sync->datagen_exit_cnt, PROC_CNT);
 
 	mems_datachck_each_pgix(PROC1_PGIX);
 
@@ -465,6 +483,7 @@ int main(int argc, char **argv)
 	test_init(argc, argv);
 
 	pstree = (struct pstree *)mmap_ashmem(PAGE_SIZE);
+	test_sync = (struct test_sync *)mmap_ashmem(sizeof(*test_sync));
 
 	struct sigaction sa = {
 		.sa_sigaction = sigchld_hand,