On 8/21/23 10:21 PM, David Marchevsky wrote:
On 8/21/23 11:18 PM, Yonghong Song wrote:
On 8/21/23 12:33 PM, Dave Marchevsky wrote:
Confirm that the following sleepable prog states fail verification:
* bpf_rcu_read_unlock before bpf_spin_unlock
* RCU CS will last at least as long as spin_lock CS
I think the reason is bpf_spin_lock() does not allow any functions
in spin lock region except some graph api kfunc's.
Yeah, agreed, this test isn't really validating anything with current verifier
logic. But, given that spin_lock CS w/ disabled preemption is an RCU CS, do
you forsee wanting to allow rcu_read_unlock within spin_lock CS?
I'll delete the test if you think it should go, but maybe it's worth
keeping with a comment summarizing why it's an interesting example.
Ya, it is an interesting case for interaction of rcu lock vs. spin lock.
I guess you can keep it with comments, unless there are some other
objections.
Also, the existing comment in that test is incorrect, will fix.
Also confirm that correct usage passes verification, specifically:
* Explicit use of bpf_rcu_read_{lock, unlock} in sleepable test prog
* Implied RCU CS due to spin_lock CS
None of the selftest progs actually attach to bpf_testmod's
bpf_testmod_test_read.
Signed-off-by: Dave Marchevsky <davemarchevsky@xxxxxx>
---
.../selftests/bpf/progs/refcounted_kptr.c | 71 +++++++++++++++++++
.../bpf/progs/refcounted_kptr_fail.c | 28 ++++++++
2 files changed, 99 insertions(+)
diff --git a/tools/testing/selftests/bpf/progs/refcounted_kptr.c b/tools/testing/selftests/bpf/progs/refcounted_kptr.c
index c55652fdc63a..893a4fdb4b6e 100644
[...]
diff --git a/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c b/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c
index 0b09e5c915b1..1ef07f6ee580 100644
--- a/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c
+++ b/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c
@@ -13,6 +13,9 @@ struct node_acquire {
struct bpf_refcount refcount;
};
+extern void bpf_rcu_read_lock(void) __ksym;
+extern void bpf_rcu_read_unlock(void) __ksym;
+
#define private(name) SEC(".data." #name) __hidden __attribute__((aligned(8)))
private(A) struct bpf_spin_lock glock;
private(A) struct bpf_rb_root groot __contains(node_acquire, node);
@@ -71,4 +74,29 @@ long rbtree_refcounted_node_ref_escapes_owning_input(void *ctx)
return 0;
}
+SEC("?fentry.s/bpf_testmod_test_read")
+__failure __msg("function calls are not allowed while holding a lock")
+int BPF_PROG(rbtree_fail_sleepable_lock_across_rcu,
+ struct file *file, struct kobject *kobj,
+ struct bin_attribute *bin_attr, char *buf, loff_t off, size_t len)
+{
+ struct node_acquire *n;
+
+ n = bpf_obj_new(typeof(*n));
+ if (!n)
+ return 0;
+
+ /* spin_{lock,unlock} are in different RCU CS */
+ bpf_rcu_read_lock();
+ bpf_spin_lock(&glock);
+ bpf_rbtree_add(&groot, &n->node, less);
+ bpf_rcu_read_unlock();
+
+ bpf_rcu_read_lock();
+ bpf_spin_unlock(&glock);
+ bpf_rcu_read_unlock();
+
+ return 0;
+}
+
char _license[] SEC("license") = "GPL";
