On 2026/6/9 15:14, Peter Zijlstra wrote:
> On Tue, Jun 09, 2026 at 08:57:28AM +0800, Tengda Wu wrote:
>> The current check in rethook_find_ret_addr() prevents obtaining a return
>> address when the target task is marked as running. However, this condition
>> is both insufficient for safety and unnecessary for its intended purpose.
>
> Depends on what safety means. If safety means not crashing, it is
> entirely superfluous. If safety means correctness, then yes, it is
> insufficient.
>
>> The check is inherently racy: a task can begin running on another CPU
>> immediately after task_is_running() returns false, potentially leading to
>> concurrent modification of rethook data structures while the iteration is
>> in progress.
>>
>> Rather than attempting to fix this unreliable check deep in the unwinding
>> path, remove it entirely. Callers that require consistency are expected
>> to provide a safe context.
>
> Perhaps also note that unwind_next() will hold RCU and the rethook_node
> things are RCU freed, so while the iteration might go off the rails and
> return invalid information, it will not crash.
>
>
>> Fixes: 54ecbe6f1ed5 ("rethook: Add a generic return hook")
>> Signed-off-by: Tengda Wu <[email protected]>
>
> With clarifications:
>
> Acked-by: Peter Zijlstra (Intel) <[email protected]>
>
Thank you for the review and suggestions, Peter.
I have incorporated your feedback into v3. The patch has been sent out.
https://lore.kernel.org/all/[email protected]/
Best regards,
Tengda
