Module Name: src Committed By: kre Date: Sun Oct 30 01:46:17 UTC 2022
Modified Files: src/bin/sh: jobs.c Log Message: PR bin/57053 is related (peripherally) here. sh has been remembering the process group of a job for a while now, but using that for almost nothing. The old way to resume a job, was to try each pid in the job with a SIGCONT (using it as the process group identifier via killpg()) until one worked (or none did, in which case resuming would be impossible, but that never actually happened). This wasn't as bad as it seems, as in practice the first process attempted was *always* the correct one. Why the loop was considered necessary I am not sure. Nothing but the first could possibly work. This worked until a fix for an obscure possible bug was added a while ago - now a process which has already finished, and had its zombie collected via wait*() is no longer ever considered to have a pid which is a candidate for use in any system call. That's because the kernel might have reassigned that pid for some newly created process (we have no idea how much time might have passed since the pid was returned to the kernel for reuse, it might have happened weeks ago). This is where the example in bin/57053 revealed a problem. That PR is really about a quite different problem in zsh (from pksrc) and should be pkg/57053, but as the test case also hit the problem here, it was assumed (by some) they were the same issue. The example is (in a small directory) ls | less which is then suspended (^Z), and resumed (fg). Since the directory is small, ls will be finished, and reaped by sh - so the code would now refuse to use its pid for the killpg() call to send the SIGCONT. The (useless) loop would attempt to use less's pid for this purpose (it is still alive at this point) but that would fail, as that pid is not a process group identifier, of anything. Hence the job could not be resumed. Before the PR (or preceding mailing list discussion) the change here had already been made (part of a much bigger set of changes, some of which might follow - sometime). We now actually use the job's remembered process group identifier when we want the process group identifier, instead of trying to guess which pid it happens to be (which actually never took any guessing, it was, and is always the pid of the first process created for the job). A couple of minor fixes to how the pgrp is obtained, and used, accompany the changes to use it when appropriate. To generate a diff of this commit: cvs rdiff -u -r1.116 -r1.117 src/bin/sh/jobs.c Please note that diffs are not public domain; they are subject to the copyright notices on the relevant files.