[PATCH bpf] bpf: fix a task_iter bug caused by a merge conflict resolution

[Yonghong Song <yhs@fb.com>]

Latest bpf tree has a bug for bpf_iter selftest.
  $ ./test_progs -n 4/25
  test_bpf_sk_storage_get:PASS:bpf_iter_bpf_sk_storage_helpers__open_and_load 0 nsec
  test_bpf_sk_storage_get:PASS:socket 0 nsec
  ...
  do_dummy_read:PASS:read 0 nsec
  test_bpf_sk_storage_get:FAIL:bpf_map_lookup_elem map value wasn't set correctly
                          (expected 1792, got -1, err=0)
  #4/25 bpf_sk_storage_get:FAIL
  #4 bpf_iter:FAIL
  Summary: 0/0 PASSED, 0 SKIPPED, 2 FAILED

When doing merge conflict resolution, Commit 4bfc4714849d missed to
save curr_task to seq_file private data. The task pointer in seq_file
private data is passed to bpf program. This caused
NULL-pointer task passed to bpf program which will immediately return
upon checking whether task pointer is NULL.

This patch added back the assignment of curr_task to seq_file private data
and fixed the issue.

Fixes: 4bfc4714849d ("Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf")
Signed-off-by: Yonghong Song <yhs@fb.com>
---
 kernel/bpf/task_iter.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 3efe38191d1c..175b7b42bfc4 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -159,6 +159,7 @@ task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info)
                 }
 
                 /* set info->task and info->tid */
+		info->task = curr_task;
 		if (curr_tid == info->tid) {
 			curr_fd = info->fd;
 		} else {
-- 
2.24.1