[PATCH bpf-next 2/3] bpf: Consolidate sleepable checks in check_kfunc_call()

[Puranjay Mohan <puranjay@kernel.org>]

check_kfunc_call() has multiple scattered checks that reject sleepable
kfuncs in various non-sleepable contexts (RCU, preempt-disabled, IRQ-
disabled). These are the same conditions already checked by
in_sleepable_context(), so replace them with a single consolidated
check.

This also simplifies the preempt lock tracking by flattening the nested
if/else structure into a linear chain: preempt_disable increments,
preempt_enable checks for underflow and decrements. The sleepable check
is kept as a separate block since it is logically distinct from the lock
accounting.

No functional change since in_sleepable_context() checks all the same
state (active_rcu_locks, active_preempt_locks, active_locks,
active_irq_id, in_sleepable).

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Mykyta Yatsenko <yatsenko@meta.com>
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
---
 kernel/bpf/verifier.c | 36 +++++++++++++-----------------------
 1 file changed, 13 insertions(+), 23 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 4e0f6be5d2d5..a9130c4888f7 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -14276,34 +14276,24 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 				}
 			}));
 		}
-	} else if (sleepable && env->cur_state->active_rcu_locks) {
-		verbose(env, "kernel func %s is sleepable within rcu_read_lock region\n", func_name);
-		return -EACCES;
-	}
-
-	if (in_rbtree_lock_required_cb(env) && (rcu_lock || rcu_unlock)) {
-		verbose(env, "Calling bpf_rcu_read_{lock,unlock} in unnecessary rbtree callback\n");
-		return -EACCES;
-	}
-
-	if (env->cur_state->active_preempt_locks) {
-		if (preempt_disable) {
-			env->cur_state->active_preempt_locks++;
-		} else if (preempt_enable) {
-			env->cur_state->active_preempt_locks--;
-		} else if (sleepable) {
-			verbose(env, "kernel func %s is sleepable within non-preemptible region\n", func_name);
-			return -EACCES;
-		}
 	} else if (preempt_disable) {
 		env->cur_state->active_preempt_locks++;
 	} else if (preempt_enable) {
-		verbose(env, "unmatched attempt to enable preemption (kernel function %s)\n", func_name);
-		return -EINVAL;
+		if (env->cur_state->active_preempt_locks == 0) {
+			verbose(env, "unmatched attempt to enable preemption (kernel function %s)\n", func_name);
+			return -EINVAL;
+		}
+		env->cur_state->active_preempt_locks--;
 	}
 
-	if (env->cur_state->active_irq_id && sleepable) {
-		verbose(env, "kernel func %s is sleepable within IRQ-disabled region\n", func_name);
+	if (sleepable && !in_sleepable_context(env)) {
+		verbose(env, "kernel func %s is sleepable within %s\n",
+			func_name, non_sleepable_context_description(env));
+		return -EACCES;
+	}
+
+	if (in_rbtree_lock_required_cb(env) && (rcu_lock || rcu_unlock)) {
+		verbose(env, "Calling bpf_rcu_read_{lock,unlock} in unnecessary rbtree callback\n");
 		return -EACCES;
 	}
 
-- 
2.52.0