coroutine: fix a use-after-free in maybe_yield #1760
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
maybe_yield_awaiter resumes the coroutine (after it decided to suspend it) by scheduling *itself* as a task, which -- when executed -- resumes the coroutine. The awaiter itself is (usually) allocated inside the coroutine frame, and dies after its containing co_await expression is resumed. This is a problem, because the reactor expects tasks to stay alive while they are running. To facilitate current_tasktrace(), a global pointer to the currently running task is needed. Thus, when the reactor starts executing a task, it saves a pointer to it in reactor::_current_task. Since the awaiter task dies immediately after returning control to its parent, reactor::_current_task is left pointing to some garbage in the coroutine frame and current_tasktrace() will (most likely) segfault when used before the next task switch. To fix this, we directly schedule the parent coroutine. Making maybe_yield_awaiter a task was an unnecessary indirection anyway. Refs scylladb#1599. It's the same kind of bug. Fixes scylladb#1759
|
@scylladb/seastar-maint hello maintainers, could you help merge this change? so we can unblock scylladb/scylladb#13730 . |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
maybe_yield_awaiter resumes the coroutine (after it decided to suspend it) by scheduling itself as a task, which -- when executed -- resumes the coroutine.
The awaiter itself is (usually) allocated inside the coroutine frame, and dies after its containing co_await expression is resumed. This is a problem, because the reactor expects tasks to stay alive while they are running. To facilitate current_tasktrace(), a global pointer to the currently running task is needed. Thus, when the reactor starts executing a task, it saves a pointer to it in reactor::_current_task.
Since the awaiter task dies immediately after returning control to its parent, reactor::_current_task is left pointing to some garbage in the coroutine frame and current_tasktrace() will (most likely) segfault when used before the next task switch.
To fix this, we directly schedule the parent coroutine. Making maybe_yield_awaiter a task was an unnecessary indirection anyway.
Refs #1599. It's the same kind of bug.
Fixes #1759