bpf: Remove now-defunct task kfuncs

In commit 22df776a9a86 ("tasks: Extract rcu_users out of union"), the
'refcount_t rcu_users' field was extracted out of a union with the
'struct rcu_head rcu' field. This allows us to safely perform a
refcount_inc_not_zero() on task->rcu_users when acquiring a reference on
a task struct. A prior patch leveraged this by making struct task_struct
an RCU-protected object in the verifier, and by bpf_task_acquire() to
use the task->rcu_users field for synchronization.

Now that we can use RCU to protect tasks, we no longer need
bpf_task_kptr_get(), or bpf_task_acquire_not_zero(). bpf_task_kptr_get()
is truly completely unnecessary, as we can just use RCU to get the
object. bpf_task_acquire_not_zero() is now equivalent to
bpf_task_acquire().

In addition to these changes, this patch also updates the associated
selftests to no longer use these kfuncs.

Signed-off-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20230331195733.699708-3-void@manifault.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 0 insertions, 73 deletions

diff --git a/tools/testing/selftests/bpf/progs/task_kfunc_failure.c b/tools/testing/selftests/bpf/progs/task_kfunc_failure.c
index 63aef547da87..dcdea3127086 100644
--- a/tools/testing/selftests/bpf/progs/task_kfunc_failure.c
+++ b/tools/testing/selftests/bpf/progs/task_kfunc_failure.c
@@ -129,59 +129,6 @@ int BPF_PROG(task_kfunc_acquire_unreleased, struct task_struct *task, u64 clone_
 }
 
 SEC("tp_btf/task_newtask")
-__failure __msg("arg#0 expected pointer to map value")
-int BPF_PROG(task_kfunc_get_non_kptr_param, struct task_struct *task, u64 clone_flags)
-{
-	struct task_struct *kptr;
-
-	/* Cannot use bpf_task_kptr_get() on a non-kptr, even on a valid task. */
-	kptr = bpf_task_kptr_get(&task);
-	if (!kptr)
-		return 0;
-
-	bpf_task_release(kptr);
-
-	return 0;
-}
-
-SEC("tp_btf/task_newtask")
-__failure __msg("arg#0 expected pointer to map value")
-int BPF_PROG(task_kfunc_get_non_kptr_acquired, struct task_struct *task, u64 clone_flags)
-{
-	struct task_struct *kptr, *acquired;
-
-	acquired = bpf_task_acquire(task);
-	if (!acquired)
-		return 0;
-
-	/* Cannot use bpf_task_kptr_get() on a non-kptr, even if it was acquired. */
-	kptr = bpf_task_kptr_get(&acquired);
-	bpf_task_release(acquired);
-	if (!kptr)
-		return 0;
-
-	bpf_task_release(kptr);
-
-	return 0;
-}
-
-SEC("tp_btf/task_newtask")
-__failure __msg("arg#0 expected pointer to map value")
-int BPF_PROG(task_kfunc_get_null, struct task_struct *task, u64 clone_flags)
-{
-	struct task_struct *kptr;
-
-	/* Cannot use bpf_task_kptr_get() on a NULL pointer. */
-	kptr = bpf_task_kptr_get(NULL);
-	if (!kptr)
-		return 0;
-
-	bpf_task_release(kptr);
-
-	return 0;
-}
-
-SEC("tp_btf/task_newtask")
 __failure __msg("Unreleased reference")
 int BPF_PROG(task_kfunc_xchg_unreleased, struct task_struct *task, u64 clone_flags)
 {
@@ -215,26 +162,6 @@ int BPF_PROG(task_kfunc_acquire_release_no_null_check, struct task_struct *task,
 }
 
 SEC("tp_btf/task_newtask")
-__failure __msg("Unreleased reference")
-int BPF_PROG(task_kfunc_get_unreleased, struct task_struct *task, u64 clone_flags)
-{
-	struct task_struct *kptr;
-	struct __tasks_kfunc_map_value *v;
-
-	v = insert_lookup_task(task);
-	if (!v)
-		return 0;
-
-	kptr = bpf_task_kptr_get(&v->task);
-	if (!kptr)
-		return 0;
-
-	/* Kptr acquired above is never released. */
-
-	return 0;
-}
-
-SEC("tp_btf/task_newtask")
 __failure __msg("Possibly NULL pointer passed to trusted arg0")
 int BPF_PROG(task_kfunc_release_untrusted, struct task_struct *task, u64 clone_flags)
 {