lightningd: parent watchman's formatted blockhash strings to tmpctx - #9363
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ksedgwic wants to merge 1 commit into
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lightningd: parent watchman's formatted blockhash strings to tmpctx#9363ksedgwic wants to merge 1 commit into
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json_add_string copies its value, so the strings fmt_bitcoin_blkid allocates in json_block_processed and json_getwatchmanheight are referenced by nothing once the call returns. They are parented to the response stream and freed with it, but the memleak scanner works by searching memory for pointers to each allocation: when a dev memleak check races an in-flight response, the unreferenced string is reported as a leak and fails the test run (seen in a liquid CI run of test_bwatch_add_watch_creates_datastore_entry). Parent them to tmpctx, the idiom used elsewhere. Fixes: ElementsProject#9362 Changelog-None
Andezion
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Aug 3, 2026
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Do you know why parenting to response specifically trips the memleak scanner here, given response is itself reachable through the command's tal tree? Is it because the scan can race a not yet completed response object mid-write?
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json_add_string copies the bytes into the stream buffer, so nothing holds a pointer to the fmt_bitcoin_blkid string once the call returns; its only tie is the tal parent link. So yes -- when a dev-memleak check lands while a response is still in flight, the string is still allocated, referenced by nothing, and gets reported. Parenting to tmpctx closes that window. |
Lagrang3
approved these changes
Aug 4, 2026
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Fixes #9362 : the memleak scanner can flag the blockhash strings
watchman formats into its RPC responses -- json_add_string copies the
value, so nothing references the string afterward, and a dev memleak
check racing an in-flight response reports it as a leak. Parent them
to tmpctx, the idiom used elsewhere.
Changelog-None