Re: [linux-next:master 7935/14039] progs/task_kfunc_failure.c:76:36: error: no member named 'last_wakee' in 'struct task_struct'

Re: [linux-next:master 7935/14039] progs/task_kfunc_failure.c:76:36: error: no member named 'last_wakee' in 'struct task_struct'

[David Vernet]

On Tue, Dec 13, 2022 at 05:35:01AM +0800, kernel test robot wrote:
> Hi David,
> 
> First bad commit (maybe != root cause):
> 
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> head:   f925116b24c0c42dc6d5ab5111c55fd7f74e8dc7
> commit: fe147956fca4604b920e6be652abc9bea8ce8952 [7935/14039] bpf/selftests: Add selftests for new task kfuncs
> compiler: gcc-11 (Debian 11.3.0-8) 11.3.0
> reproduce:
>         # https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=fe147956fca4604b920e6be652abc9bea8ce8952
>         git remote add linux-next https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
>         git fetch --no-tags linux-next master
>         git checkout fe147956fca4604b920e6be652abc9bea8ce8952
>         make O=/tmp/kselftest headers
>         make O=/tmp/kselftest -C tools/testing/selftests
> 
> If you fix the issue, kindly add following tag where applicable
> | Reported-by: kernel test robot <lkp@intel.com>

Ah, task->last_wakee isn't defined on UP builds, my mistake. This patch
fixes the issue. I'll send the patch to the bpf list in a separate
email.

From 80ec7fa20b0beb1b047bfc66b49b0910c578da83 Mon Sep 17 00:00:00 2001
From: David Vernet <void@manifault.com>
Date: Mon, 12 Dec 2022 17:34:40 -0600
Subject: [PATCH bpf-next] bpf/selftests: Use parent instead of last_wakee in
 task kfunc test

Commit fe147956fca4 ("bpf/selftests: Add selftests for new task kfuncs")
added a negative selftest called task_kfunc_acquire_trusted_walked which
ensures that a BPF program that gets a struct task_struct * pointer from
walking a struct is properly rejected by the verifier if it tries to
pass that pointer to a task kfunc. In order to do this, it uses
task->last_wakee, but unfortunately that's not defined on UP builds.
Just use task->parent instead.

Reported-by: kernel test robot <lkp@intel.com>
Fixes: fe147956fca4 ("bpf/selftests: Add selftests for new task kfuncs")
Signed-off-by: David Vernet <void@manifault.com>
---
 tools/testing/selftests/bpf/progs/task_kfunc_failure.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/progs/task_kfunc_failure.c b/tools/testing/selftests/bpf/progs/task_kfunc_failure.c
index 87fa1db9d9b5..60508c20041f 100644
--- a/tools/testing/selftests/bpf/progs/task_kfunc_failure.c
+++ b/tools/testing/selftests/bpf/progs/task_kfunc_failure.c
@@ -73,7 +73,7 @@ int BPF_PROG(task_kfunc_acquire_trusted_walked, struct task_struct *task, u64 cl
        struct task_struct *acquired;

        /* Can't invoke bpf_task_acquire() on a trusted pointer obtained from walking a struct. */
-       acquired = bpf_task_acquire(task->last_wakee);
+       acquired = bpf_task_acquire(task->parent);
        bpf_task_release(acquired);

        return 0;
--
2.38.1