Re: [PATCH bpf-next] bpf: Fix a typo in comment for DFS algorithm

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On 10/26/2022 2:32 PM, Alexei Starovoitov wrote:
On Tue, Oct 25, 2022 at 7:42 PM Xu Kuohai <xukuohai@xxxxxxxxxxxxxxx> wrote:

From: Xu Kuohai <xukuohai@xxxxxxxxxx>

There is a typo in comment for DFS algorithm in bpf/verifier.c. The top
element should not be popped until all its neighbors have been checked.
Fix it.

Fixes: 475fb78fbf48 ("bpf: verifier (add branch/goto checks)")
Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
---
  kernel/bpf/verifier.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index b83a8d420520..96ba5ea6d1a6 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10662,7 +10662,7 @@ static int check_return_code(struct bpf_verifier_env *env)
   * 3      let S be a stack
   * 4      S.push(v)
   * 5      while S is not empty
- * 6            t <- S.pop()
+ * 6            t <- S.top()

Even with this fix the comment is not quite accurate.
I wonder whether we should keep it or delete it completely.

The comment describes the non-recursive DFS algorithm used by the C code.
Although it does not describe the full details, it helps us to understand
the code, so I think it should be kept.

At least please use 'peek' instead of 'top'.

OK.



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