Merge branch 'bpf: Avoid unnecessary deadlock detection and failure in task storage'

Martin KaFai Lau says:

====================

From: Martin KaFai Lau <martin.lau@kernel.org>

The commit bc235cdb423a ("bpf: Prevent deadlock from recursive bpf_task_storage_[get|delete]")
added deadlock detection to avoid a tracing program from recurring
on the bpf_task_storage_{get,delete}() helpers.  These helpers acquire
a spin lock and it will lead to deadlock.

It is unnecessary for the bpf_lsm and bpf_iter programs which do
not recur.  The situation is the same as the existing
bpf_pid_task_storage_{lookup,delete}_elem() which are
used in the syscall and they also do not have deadlock detection.

This set is to add new bpf_task_storage_{get,delete}() helper proto
without the deadlock detection.  The set also removes the prog->active
check from the bpf_lsm and bpf_iter program.  Please see the individual
patch for details.
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 47 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/task_storage_nodeadlock.c b/tools/testing/selftests/bpf/progs/task_storage_nodeadlock.c
new file mode 100644
index 000000000000..ea2dbb80f7b3
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/task_storage_nodeadlock.c
@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+#ifndef EBUSY
+#define EBUSY 16
+#endif
+
+extern bool CONFIG_PREEMPT __kconfig __weak;
+int nr_get_errs = 0;
+int nr_del_errs = 0;
+
+struct {
+	__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__type(key, int);
+	__type(value, int);
+} task_storage SEC(".maps");
+
+SEC("lsm.s/socket_post_create")
+int BPF_PROG(socket_post_create, struct socket *sock, int family, int type,
+	     int protocol, int kern)
+{
+	struct task_struct *task;
+	int ret, zero = 0;
+	int *value;
+
+	if (!CONFIG_PREEMPT)
+		return 0;
+
+	task = bpf_get_current_task_btf();
+	value = bpf_task_storage_get(&task_storage, task, &zero,
+				     BPF_LOCAL_STORAGE_GET_F_CREATE);
+	if (!value)
+		__sync_fetch_and_add(&nr_get_errs, 1);
+
+	ret = bpf_task_storage_delete(&task_storage,
+				      bpf_get_current_task_btf());
+	if (ret == -EBUSY)
+		__sync_fetch_and_add(&nr_del_errs, 1);
+
+	return 0;
+}