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The reaper finds a process that left an exec's group by the exec id in its environment. A process in the middle of an execve has no environment to read: from the moment the new image's memory replaces the old until its arguments and environment are laid out, the kernel answers an empty one (a probe reading /proc/<pid>/environ of a process that execs in a loop got an empty answer in 3,341 of 20,000 reads). A leftover is often right there when a round comes: `cmd &` and the command's exit are an instant apart, and `setsid cmd` is two execs. The SIGTERM round counted such a process as untagged and skipped it; only the SIGKILL round, SIGKILL_GRACE_MS later, ended it. That is how exec-completion.test.ts failed on CI (#4445, Checks run 37752204357): its final barrier gave the reaper five seconds to end the `setsid sleep 60` a finished exec left, and the SIGKILL round came a few milliseconds after that. The test now waits for the reaper's own bound (the SIGKILL grace plus the scan deadline), and the scan reads an empty environment again, four times ten milliseconds apart, before the process counts as untagged; a process whose environment really is empty costs a scan that long. No user-visible change: no messages, docs under docs/ or READMEs.
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Diagnostic read; findings are on #4531. Branch deleted. |
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Throwaway diagnostic for the exec-completion failure seen on #4445 (Checks runs 37752204357 and 37782005524). Runs the setsid-survivor scenario 12 times on the CI runner and fails on purpose with a report of which signals reached the survivor and when. Will be closed and the branch deleted once read. Not for merge.