bpf: Report rqspinlock deadlocks/timeout to BPF stderr

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

Reviewed-by: Emil Tsalapatis <[email protected]>
Signed-off-by: Kumar Kartikeya Dwivedi <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: kkdwivedi

kernel/bpf/rqspinlock.c

@@ -666,6 +666,27 @@ 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_stream_stage ss;
+	struct bpf_prog *prog;
+
+	prog = bpf_prog_find_from_stack();
+	if (!prog)
+		return;
+	bpf_stream_stage(ss, prog, BPF_STDERR, ({
+		bpf_stream_printk(ss, "ERROR: %s for bpf_res_spin_lock%s\n", str, irqsave ? "_irqsave" : "");
+		bpf_stream_printk(ss, "Attempted lock   = 0x%px\n", lock);
+		bpf_stream_printk(ss, "Total held locks = %d\n", rqh->cnt);
+		for (int i = 0; i < min(RES_NR_HELD, rqh->cnt); i++)
+			bpf_stream_printk(ss, "Held lock[%2d] = 0x%px\n", i, rqh->locks[i]);
+		bpf_stream_dump_stack(ss);
+	}));
+}
+
+#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 +697,7 @@ __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 +720,7 @@ __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;