[PATCH v2 07/23] mm: introduce bpf_oom_kill_process() bpf kfunc

[Roman Gushchin <roman.gushchin@linux.dev>]

Introduce bpf_oom_kill_process() bpf kfunc, which is supposed
to be used by BPF OOM programs. It allows to kill a process
in exactly the same way the OOM killer does: using the OOM reaper,
bumping corresponding memcg and global statistics, respecting
memory.oom.group etc.

On success, it sets om_control's bpf_memory_freed field to true,
enabling the bpf program to bypass the kernel OOM killer.

Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
---
 mm/oom_kill.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 67 insertions(+)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index d05ec0f84087..3c86cd755371 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -1288,3 +1288,70 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags)
 	return -ENOSYS;
 #endif /* CONFIG_MMU */
 }
+
+#ifdef CONFIG_BPF_SYSCALL
+
+__bpf_kfunc_start_defs();
+/**
+ * bpf_oom_kill_process - Kill a process as OOM killer
+ * @oc: pointer to oom_control structure, describes OOM context
+ * @task: task to be killed
+ * @message__str: message to print in dmesg
+ *
+ * Kill a process in a way similar to the kernel OOM killer.
+ * This means dump the necessary information to dmesg, adjust memcg
+ * statistics, leverage the oom reaper, respect memory.oom.group etc.
+ *
+ * bpf_oom_kill_process() marks the forward progress by setting
+ * oc->bpf_memory_freed. If the progress was made, the bpf program
+ * is free to decide if the kernel oom killer should be invoked.
+ * Otherwise it's enforced, so that a bad bpf program can't
+ * deadlock the machine on memory.
+ */
+__bpf_kfunc int bpf_oom_kill_process(struct oom_control *oc,
+				     struct task_struct *task,
+				     const char *message__str)
+{
+	if (oom_unkillable_task(task))
+		return -EPERM;
+
+	/* paired with put_task_struct() in oom_kill_process() */
+	task = tryget_task_struct(task);
+	if (!task)
+		return -EINVAL;
+
+	oc->chosen = task;
+
+	oom_kill_process(oc, message__str);
+
+	oc->chosen = NULL;
+	oc->bpf_memory_freed = true;
+
+	return 0;
+}
+
+__bpf_kfunc_end_defs();
+
+BTF_KFUNCS_START(bpf_oom_kfuncs)
+BTF_ID_FLAGS(func, bpf_oom_kill_process, KF_SLEEPABLE | KF_TRUSTED_ARGS)
+BTF_KFUNCS_END(bpf_oom_kfuncs)
+
+static const struct btf_kfunc_id_set bpf_oom_kfunc_set = {
+	.owner          = THIS_MODULE,
+	.set            = &bpf_oom_kfuncs,
+};
+
+static int __init bpf_oom_init(void)
+{
+	int err;
+
+	err = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS,
+					&bpf_oom_kfunc_set);
+	if (err)
+		pr_warn("error while registering bpf oom kfuncs: %d", err);
+
+	return err;
+}
+late_initcall(bpf_oom_init);
+
+#endif
-- 
2.51.0