common: guard ecdh() against HSM fd being non-blocking - #9402
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common: guard ecdh() against HSM fd being non-blocking#9402daywalker90 wants to merge 2 commits into
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On macOS under load, connectd intermittently dies with "STATUS_FAIL_HSM_IO: No hsmd ECDH response". hsmd logs that it received WIRE_HSMD_ECDH_REQ, yet connectd's synchronous wire_sync_read() returns NULL. The only way that read fails after hsmd answered is an EAGAIN from an O_NONBLOCK HSM fd. The HSM fd is one end of a socketpair sent hsmd -> lightningd -> connectd via SCM_RIGHTS; the other end lives in hsmd's io loop, whose io_new_conn() sets O_NONBLOCK (io.c:io_new_conn -> io_fd_block(fd, false)). On macOS the flag follows the shared open file description across SCM_RIGHTS, so it can be flipped on after the one-shot setup-time io_fd_block(hsm_fd, true) added in the previous fix, re-introducing the EAGAIN. Ubuntu is unaffected because its fd semantics keep the descriptions independent. Fix ecdh() itself so it does not depend on the fd flag state: re-assert blocking at the start of every synchronous exchange, and if a non-blocking read still returns EAGAIN, poll for the response and retry instead of failing the daemon. This also hardens channeld, which uses the same ecdh()/ecdh_hsmd_setup() path. Changelog-Fixed: connectd: fix intermittent "No hsmd ECDH response" crash on macOS under load (issue ElementsProject#9060).
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Fixes: #9323