Bugfix: bthread_interrupt was scheduled to the wrong tag group

[chenBright]

What problem does this PR solve?

Issue Number: resolve #3349

Problem Summary:

bthread_stop() calls bthread_interrupt(tid), which uses the default
argument BTHREAD_TAG_DEFAULT = 0. When a non-worker thread (e.g. the
main thread during Server::~Server() -> Join()) stops a bthread with tag > 0,
TaskGroup::interrupt() takes the c->choose_one_group(tag)->ready_to_run_remote(m)
path with tag == 0. As a result, the interrupted bthread is re-scheduled onto a
worker of tag 0 instead of its own tag group, breaking tag isolation.

What is changed and the side effects?

Changed:

The tag of a bthread is already recorded in its TaskMeta
(m->attr.tag), so passing the tag explicitly is unnecessary and
error-prone. Instead of forwarding the (default) tag argument, the code
now reads the tag from the target TaskMeta:

• bthread_interrupt(bthread_t, bthread_tag_t): the tag parameter is
  now ignored (kept only for API/ABI compatibility) and the call
  delegates to TaskGroup::interrupt(tid, control).
• TaskGroup::interrupt(): the tag parameter is removed; the target
  group is chosen via c->choose_one_group(m->attr.tag).
• butex.cpp: the redundant ButexBthreadWaiter::tag field is removed;
  butex_wake, butex_wake_n, butex_wake_except, butex_requeue and
  erase_from_butex now obtain the tag from task_meta->attr.tag.

Side effects:

• Performance effects:

• Breaking backward compatibility:

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Check List:

• Please make sure your changes are compilable.
• When providing us with a new feature, it is best to add related tests.
• Please follow Contributor Covenant Code of Conduct.

[Copilot]

Pull request overview

Fixes incorrect tag-group scheduling when interrupting/stopping bthreads from non-worker threads (e.g., Server::~Server()->Join()), aiming to preserve tag isolation by selecting the target TaskGroup based on the interrupted bthread’s tag.

Changes:

• Removes the tag argument from TaskGroup::interrupt() and switches remote re-scheduling to use the target task’s recorded tag.
• Keeps bthread_interrupt(bthread_t, bthread_tag_t) for API/ABI compatibility but ignores the tag parameter internally.
• Removes ButexBthreadWaiter::tag and routes butex wake/requeue scheduling via task_meta->attr.tag.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 6 comments.

File	Description
src/bthread/task_group.h	Updates TaskGroup::interrupt signature to remove the tag parameter.
src/bthread/task_group.cpp	Chooses remote task group for interrupted sleepers based on the target task’s tag.
src/bthread/butex.cpp	Removes stored waiter tag and attempts to schedule wakeups using task_meta->attr.tag.
src/bthread/bthread.cpp	Keeps bthread_interrupt signature but forwards to the new TaskGroup::interrupt overload.

Comments suppressed due to low confidence (1)

src/bthread/task_group.cpp:1096

• The change routes interruption/wakeup scheduling based on a tag, but there’s no unit test covering the reported regression scenario (non-worker thread stops a sleeping bthread with tag>0 and it must be rescheduled within the same tag group). Adding a test would help prevent future regressions in tag isolation for bthread_stop()/bthread_interrupt() and the usleep/butex wake paths.

int TaskGroup::interrupt(bthread_t tid, TaskControl* c) {
    // Consume current_waiter in the TaskMeta, wake it up then set it back.
    ButexWaiter* w = NULL;
    uint64_t sleep_id = 0;
    int rc = interrupt_and_consume_waiters(tid, &w, &sleep_id);

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