[PATCH bpf-next] bpf: fix raw_tp test run in preempt kernel

[Song Liu]

In preempt kernel, BPF_PROG_TEST_RUN on raw_tp triggers:

[   35.874974] BUG: using smp_processor_id() in preemptible [00000000]
code: new_name/87
[   35.893983] caller is bpf_prog_test_run_raw_tp+0xd4/0x1b0
[   35.900124] CPU: 1 PID: 87 Comm: new_name Not tainted 5.9.0-rc6-g615bd02bf #1
[   35.907358] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 1.10.2-1ubuntu1 04/01/2014
[   35.916941] Call Trace:
[   35.919660]  dump_stack+0x77/0x9b
[   35.923273]  check_preemption_disabled+0xb4/0xc0
[   35.928376]  bpf_prog_test_run_raw_tp+0xd4/0x1b0
[   35.933872]  ? selinux_bpf+0xd/0x70
[   35.937532]  __do_sys_bpf+0x6bb/0x21e0
[   35.941570]  ? find_held_lock+0x2d/0x90
[   35.945687]  ? vfs_write+0x150/0x220
[   35.949586]  do_syscall_64+0x2d/0x40
[   35.953443]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fix this by calling migrate_disable() before smp_processor_id().

Fixes: 1b4d60ec162f ("bpf: Enable BPF_PROG_TEST_RUN for raw_tracepoint")
Reported-by: Alexei Starovoitov <a...@kernel.org>
Signed-off-by: Song Liu <songliubrav...@fb.com>
---
 net/bpf/test_run.c | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index fde5db93507c4..3ea05a5daf544 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -251,11 +251,7 @@ __bpf_prog_test_run_raw_tp(void *data)
 {
        struct bpf_raw_tp_test_run_info *info = data;
 
-       rcu_read_lock();
-       migrate_disable();
        info->retval = BPF_PROG_RUN(info->prog, info->ctx);
-       migrate_enable();
-       rcu_read_unlock();
 }
 
 int bpf_prog_test_run_raw_tp(struct bpf_prog *prog,
@@ -293,27 +289,27 @@ int bpf_prog_test_run_raw_tp(struct bpf_prog *prog,
 
        info.prog = prog;
 
+       rcu_read_lock();
+       migrate_disable();
        if ((kattr->test.flags & BPF_F_TEST_RUN_ON_CPU) == 0 ||
            cpu == smp_processor_id()) {
                __bpf_prog_test_run_raw_tp(&info);
-       } else {
+       } else if (cpu >= nr_cpu_ids || !cpu_online(cpu)) {
                /* smp_call_function_single() also checks cpu_online()
                 * after csd_lock(). However, since cpu is from user
                 * space, let's do an extra quick check to filter out
                 * invalid value before smp_call_function_single().
                 */
-               if (cpu >= nr_cpu_ids || !cpu_online(cpu)) {
                err = -ENXIO;
-                       goto out;
-               }
-
+       } else {
                err = smp_call_function_single(cpu, __bpf_prog_test_run_raw_tp,
                                               &info, 1);
-               if (err)
-                       goto out;
        }
+       migrate_enable();
+       rcu_read_unlock();
 
-       if (copy_to_user(&uattr->test.retval, &info.retval, sizeof(u32)))
+       if (err == 0 &&
+           copy_to_user(&uattr->test.retval, &info.retval, sizeof(u32)))
                err = -EFAULT;
 
 out:
-- 
2.24.1