From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D06A38F45 for ; Tue, 22 Aug 2023 15:00:22 +0000 (UTC) Received: from out-60.mta0.migadu.com (out-60.mta0.migadu.com [IPv6:2001:41d0:1004:224b::3c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B45D9126 for ; Tue, 22 Aug 2023 08:00:20 -0700 (PDT) Message-ID: <32967c1b-7af1-195d-966b-87a2187a179e@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1692716418; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=69PEvtrhyFmFyrHKiq9+ub6td25S4c8BIAxrwoVRgrw=; b=ab8657sVZfI6meiFLUFzJ+s1yJuEDxGOu6a1D4tD3eZp1aKPoaHk7abdqpxu2KChmgYIDA kH02MidFvvvnEYh4iG/4pmYL19Un9bqwfwE/RLibnFu9ZIZoA8y7d1c4AJyZEjiPwv+l+g uGd6aLw7i7A6AyjvKGGxb4aMk+fbmdU= Date: Tue, 22 Aug 2023 08:00:09 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Reply-To: yonghong.song@linux.dev Subject: Re: [PATCH v2 bpf-next 7/7] selftests/bpf: Add tests for rbtree API interaction in sleepable progs Content-Language: en-US To: David Marchevsky , Dave Marchevsky , bpf@vger.kernel.org Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Kernel Team References: <20230821193311.3290257-1-davemarchevsky@fb.com> <20230821193311.3290257-8-davemarchevsky@fb.com> <7aaa5d24-1377-48c4-1ace-b6a2fc79a2d0@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_BLOCKED, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net 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 >>> --- >>>   .../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";