[RFC PATCH bpf-next/net v1 10/13] bpf: Report rqspinlock deadlocks/timeout to BPF stderr

[Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>]

Begin reporting rqspinlock deadlocks and timeout to BPF program's
stderr.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
---
 kernel/bpf/rqspinlock.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index b896c4a75a5c..7cf6bd8e4f78 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -666,6 +666,26 @@ EXPORT_SYMBOL_GPL(resilient_queued_spin_lock_slowpath);
 
 __bpf_kfunc_start_defs();
 
+static void bpf_prog_report_rqspinlock_violation(const char *str, void *lock, bool irqsave)
+{
+	struct rqspinlock_held *rqh = this_cpu_ptr(&rqspinlock_held_locks);
+	struct bpf_prog *prog;
+
+	prog = bpf_prog_find_from_stack();
+	if (!prog)
+		return;
+	if (atomic_long_fetch_add(1, &prog->aux->error_count) >= BPF_PROG_ERROR_COUNT_MAX)
+		return;
+	bpf_prog_stderr_printk(prog, "ERROR: %s for bpf_res_spin_lock%s\n", str, irqsave ? "_irqsave" : "");
+	bpf_prog_stderr_printk(prog, "Attempted lock   = 0x%px\n", lock);
+	bpf_prog_stderr_printk(prog, "Total held locks = %d\n", rqh->cnt);
+	for (int i = 0; i < min(RES_NR_HELD, rqh->cnt); i++)
+		bpf_prog_stderr_printk(prog, "Held lock[%2d] = 0x%px\n", i, rqh->locks[i]);
+	bpf_prog_stderr_dump_stack(prog);
+}
+
+#define REPORT_STR(ret) ({ (ret) == -ETIMEDOUT ? "Timeout detected" : "AA or ABBA deadlock detected"; })
+
 __bpf_kfunc int bpf_res_spin_lock(struct bpf_res_spin_lock *lock)
 {
 	int ret;
@@ -676,6 +696,7 @@ __bpf_kfunc int bpf_res_spin_lock(struct bpf_res_spin_lock *lock)
 	preempt_disable();
 	ret = res_spin_lock((rqspinlock_t *)lock);
 	if (unlikely(ret)) {
+		bpf_prog_report_rqspinlock_violation(REPORT_STR(ret), lock, false);
 		preempt_enable();
 		return ret;
 	}
@@ -698,6 +719,7 @@ __bpf_kfunc int bpf_res_spin_lock_irqsave(struct bpf_res_spin_lock *lock, unsign
 	local_irq_save(flags);
 	ret = res_spin_lock((rqspinlock_t *)lock);
 	if (unlikely(ret)) {
+		bpf_prog_report_rqspinlock_violation(REPORT_STR(ret), lock, true);
 		local_irq_restore(flags);
 		preempt_enable();
 		return ret;
-- 
2.47.1