Fix IOBuf TLS block pool self-loop caused by double-return (#3243)#3244
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walterzhaoJR wants to merge 3 commits intoapache:masterfrom
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Fix IOBuf TLS block pool self-loop caused by double-return (#3243)#3244walterzhaoJR wants to merge 3 commits intoapache:masterfrom
walterzhaoJR wants to merge 3 commits intoapache:masterfrom
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release_tls_block() and release_tls_block_chain() do not guard against a block being returned to TLS when it is already the list head. The assignment `b->portal_next = block_head` becomes `b->portal_next = b`, forming a self-loop that causes remove_tls_block_chain() or share_tls_block() to spin forever, silently hanging the thread at exit. Fix: - release_tls_block(): add early return when b == block_head, skipping the duplicate insertion. - release_tls_block_chain(): during the existing chain walk, check each node against block_head before linking. Return early if overlap is detected so that num_blocks stays consistent with the actual list length (remove_tls_block_chain verifies this via CHECK_EQ). Add three unit tests that reproduce the self-loop through: 1. Direct double release_tls_block() of the same block. 2. release_tls_block_chain() with a chain overlapping the TLS head. 3. IOBufAsZeroCopyOutputStream::BackUp() followed by a second release.
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Pull request overview
Fixes a TLS IOBuf block-pool corruption case where double-returning a block can create a cyclic free-list and hang the thread on later traversal (notably at thread exit cleanup).
Changes:
- Add a guard in
release_tls_block()intended to prevent re-inserting the TLS head and forming a self-loop. - Add an overlap check in
release_tls_block_chain()intended to prevent linking a chain that would create a cycle and to keepnum_blocksconsistent. - Add three unit tests reproducing the reported hang scenarios from issue #3243.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 9 comments.
| File | Description |
|---|---|
src/butil/iobuf_inl.h |
Adds a duplicate-return guard in release_tls_block() to prevent self-looping the TLS free list. |
src/butil/iobuf.cpp |
Adds an overlap check and uses a saved old_head when returning a block chain to TLS. |
test/iobuf_unittest.cpp |
Adds regression tests that attempt to reproduce and detect the TLS free-list cycle described in #3243. |
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release_tls_block() and release_tls_block_chain() do not guard against a block being returned to TLS when it is already the list head. The assignment
b->portal_next = block_headbecomesb->portal_next = b, forming a self-loop that causes remove_tls_block_chain() or share_tls_block() to spin forever, silently hanging the thread at exit.Fix:
Add three unit tests that reproduce the self-loop through:
What problem does this PR solve?
Issue Number: resolve
Problem Summary:
What is changed and the side effects?
Changed:
Side effects:
Performance effects:
Breaking backward compatibility:
Check List: