bpf: Fix test_lru_sanity5() in test_lru_map.c

test_lru_sanity5() fails when the number of online cpus
is fewer than the number of possible cpus.  It can be
reproduced with qemu by using cmd args "--smp cpus=2,maxcpus=8".

The problem is the loop in test_lru_sanity5() is testing
'i' which is incorrect.

This patch:
1. Make sched_next_online() always return -1 if it cannot
   find a next cpu to schedule the process.
2. In test_lru_sanity5(), the parent process does
   sched_setaffinity() first (through sched_next_online())
   and the forked process will inherit it according to
   the 'man sched_setaffinity'.

Fixes: 5db58faf989f ("bpf: Add tests for the LRU bpf_htab")
Reported-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 27 insertions, 26 deletions

diff --git a/tools/testing/selftests/bpf/test_lru_map.c b/tools/testing/selftests/bpf/test_lru_map.c
index b13fed534d76..9f7bd1915c21 100644
--- a/tools/testing/selftests/bpf/test_lru_map.c
+++ b/tools/testing/selftests/bpf/test_lru_map.c
@@ -67,21 +67,23 @@ static int map_equal(int lru_map, int expected)
         return map_subset(lru_map, expected) && map_subset(expected, lru_map);
 }
 
-static int sched_next_online(int pid, int next_to_try)
+static int sched_next_online(int pid, int *next_to_try)
 {
         cpu_set_t cpuset;
+        int next = *next_to_try;
+        int ret = -1;
 
-        if (next_to_try == nr_cpus)
-                return -1;
-
-        while (next_to_try < nr_cpus) {
+        while (next < nr_cpus) {
                 CPU_ZERO(&cpuset);
-                CPU_SET(next_to_try++, &cpuset);
-                if (!sched_setaffinity(pid, sizeof(cpuset), &cpuset))
+                CPU_SET(next++, &cpuset);
+                if (!sched_setaffinity(pid, sizeof(cpuset), &cpuset)) {
+                        ret = 0;
                         break;
+                }
         }
 
-        return next_to_try;
+        *next_to_try = next;
+        return ret;
 }
 
 /* Size of the LRU amp is 2
@@ -96,11 +98,12 @@ static void test_lru_sanity0(int map_type, int map_flags)
 {
         unsigned long long key, value[nr_cpus];
         int lru_map_fd, expected_map_fd;
+        int next_cpu = 0;
 
         printf("%s (map_type:%d map_flags:0x%X): ", __func__, map_type,
                map_flags);
 
-        assert(sched_next_online(0, 0) != -1);
+        assert(sched_next_online(0, &next_cpu) != -1);
 
         if (map_flags & BPF_F_NO_COMMON_LRU)
                 lru_map_fd = create_map(map_type, map_flags, 2 * nr_cpus);
@@ -183,6 +186,7 @@ static void test_lru_sanity1(int map_type, int map_flags, unsigned int tgt_free)
         int lru_map_fd, expected_map_fd;
         unsigned int batch_size;
         unsigned int map_size;
+        int next_cpu = 0;
 
         if (map_flags & BPF_F_NO_COMMON_LRU)
                 /* Ther percpu lru list (i.e each cpu has its own LRU
@@ -196,7 +200,7 @@ static void test_lru_sanity1(int map_type, int map_flags, unsigned int tgt_free)
         printf("%s (map_type:%d map_flags:0x%X): ", __func__, map_type,
                map_flags);
 
-        assert(sched_next_online(0, 0) != -1);
+        assert(sched_next_online(0, &next_cpu) != -1);
 
         batch_size = tgt_free / 2;
         assert(batch_size * 2 == tgt_free);
@@ -262,6 +266,7 @@ static void test_lru_sanity2(int map_type, int map_flags, unsigned int tgt_free)
         int lru_map_fd, expected_map_fd;
         unsigned int batch_size;
         unsigned int map_size;
+        int next_cpu = 0;
 
         if (map_flags & BPF_F_NO_COMMON_LRU)
                 /* Ther percpu lru list (i.e each cpu has its own LRU
@@ -275,7 +280,7 @@ static void test_lru_sanity2(int map_type, int map_flags, unsigned int tgt_free)
         printf("%s (map_type:%d map_flags:0x%X): ", __func__, map_type,
                map_flags);
 
-        assert(sched_next_online(0, 0) != -1);
+        assert(sched_next_online(0, &next_cpu) != -1);
 
         batch_size = tgt_free / 2;
         assert(batch_size * 2 == tgt_free);
@@ -370,11 +375,12 @@ static void test_lru_sanity3(int map_type, int map_flags, unsigned int tgt_free)
         int lru_map_fd, expected_map_fd;
         unsigned int batch_size;
         unsigned int map_size;
+        int next_cpu = 0;
 
         printf("%s (map_type:%d map_flags:0x%X): ", __func__, map_type,
                map_flags);
 
-        assert(sched_next_online(0, 0) != -1);
+        assert(sched_next_online(0, &next_cpu) != -1);
 
         batch_size = tgt_free / 2;
         assert(batch_size * 2 == tgt_free);
@@ -430,11 +436,12 @@ static void test_lru_sanity4(int map_type, int map_flags, unsigned int tgt_free)
         int lru_map_fd, expected_map_fd;
         unsigned long long key, value[nr_cpus];
         unsigned long long end_key;
+        int next_cpu = 0;
 
         printf("%s (map_type:%d map_flags:0x%X): ", __func__, map_type,
                map_flags);
 
-        assert(sched_next_online(0, 0) != -1);
+        assert(sched_next_online(0, &next_cpu) != -1);
 
         if (map_flags & BPF_F_NO_COMMON_LRU)
                 lru_map_fd = create_map(map_type, map_flags,
@@ -502,9 +509,8 @@ static void do_test_lru_sanity5(unsigned long long last_key, int map_fd)
 static void test_lru_sanity5(int map_type, int map_flags)
 {
         unsigned long long key, value[nr_cpus];
-        int next_sched_cpu = 0;
+        int next_cpu = 0;
         int map_fd;
-        int i;
 
         if (map_flags & BPF_F_NO_COMMON_LRU)
                 return;
@@ -519,27 +525,20 @@ static void test_lru_sanity5(int map_type, int map_flags)
         key = 0;
         assert(!bpf_map_update(map_fd, &key, value, BPF_NOEXIST));
 
-        for (i = 0; i < nr_cpus; i++) {
+        while (sched_next_online(0, &next_cpu) != -1) {
                 pid_t pid;
 
                 pid = fork();
                 if (pid == 0) {
-                        next_sched_cpu = sched_next_online(0, next_sched_cpu);
-                        if (next_sched_cpu != -1)
-                                do_test_lru_sanity5(key, map_fd);
+                        do_test_lru_sanity5(key, map_fd);
                         exit(0);
                 } else if (pid == -1) {
-                        printf("couldn't spawn #%d process\n", i);
+                        printf("couldn't spawn process to test key:%llu\n",
+                               key);
                         exit(1);
                 } else {
                         int status;
 
-                        /* It is mostly redundant and just allow the parent
-                         * process to update next_shced_cpu for the next child
-                         * process
-                         */
-                        next_sched_cpu = sched_next_online(pid, next_sched_cpu);
-
                         assert(waitpid(pid, &status, 0) == pid);
                         assert(status == 0);
                         key++;
@@ -547,6 +546,8 @@ static void test_lru_sanity5(int map_type, int map_flags)
         }
 
         close(map_fd);
+        /* At least one key should be tested */
+        assert(key > 0);
 
         printf("Pass\n");
 }