Re: [PATCH] function_graph: Use the saved entry's size when reprinting it

[Donggeun Yoo]

On Sun, Sep 06, 2026 at 04:02:47AM +0000, sashiko-bot@xxxxxxxxxx wrote:
> - [High] This problem wasn't introduced by this patch, but state
> desynchronization when reprinting a previously failed trace entry causes
> the current entry in the ring buffer to be incorrectly consumed and
> permanently dropped.

print_graph_entry() does not always return TRACE_TYPE_HANDLED.
print_graph_entry_nested() returns TRACE_TYPE_NO_CONSUME, for the reason
given in the comment above it, so the quoted branch is not reached in the
nested case.

For a leaf, print_graph_entry_leaf() has printed the entry and its return
as one line, so the entry left at the head has already been shown and
consuming it is correct, as it is on the normal path. The iter->cpu != cpu
test is what separates the two: on another CPU the head is not the return
of the pair just reprinted, so it is left alone and ignore is set for it
instead.

The other two are pre-existing, and I looked at both while working on this
patch. get_return_for_leaf() returning at !event has already consumed the
entry, so failing there leaves data->failed set over a copy from an earlier
pass. I saw that once in about 30000 replays but could not pin any output
on it, so I have not sent a fix; say the word if you would rather have one
on the reachability argument alone. The static on ret in
print_graph_entry() has no reason to be there, though I found nothing that
misbehaves.

Thanks,
Donggeun