[v3] jobs - Do not block when waiting on SIGCHLD

Commit Message

Herbert Xu May 6, 2018, 4:40 p.m. UTC

On Mon, May 07, 2018 at 12:24:49AM +0800, Herbert Xu wrote:
>
> However, a bigger issue is that the original fix was incomplete.
> In particular, multiple jobs may have exited when gotsigchld is
> set.  But the loop will exit after just waiting for one job if
> no new jobs exit triggering a new SIGCHLD.

In fact there is another regression with the original patch:
foreground jobs may trigger a showjob() if interrupted by SIGINT.

So here is a new version.

---8<---
Because of the nature of SIGCHLD, the process may have already been
waited on and therefore we must be prepared for the case that wait
may block.  So ensure that it doesn't by using WNOHANG.

Furthermore, multiple jobs may have exited when gotsigchld is set.
Therefore we need to wait until there are no zombies left.

Lastly, waitforjob needs to be called with interrupts off and
the original patch broke that.

Fixes: 03876c0743a5 ("eval: Reap zombies after built-in...")
Signed-off-by: Herbert Xu <[e-mail]>

Patch

diff --git a/src/eval.c b/src/eval.c
index a27d657..39c4e41 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -859,10 +859,8 @@  bail:
 		if (!(flags & EV_EXIT) || have_traps()) {
 			INTOFF;
 			jp = makejob(cmd, 1);
-			if (forkshell(jp, cmd, FORK_FG) != 0) {
-				INTON;
+			if (forkshell(jp, cmd, FORK_FG) != 0)
 				break;
-			}
 			FORCEINTON;
 		}
 		listsetvar(varlist.list, VEXPORT|VSTACK);
@@ -875,11 +873,8 @@  bail:
 			if (execcmd && argc > 1)
 				listsetvar(varlist.list, VEXPORT);
 		}
-		if (evalbltin(cmdentry.u.cmd, argc, argv, flags)) {
-			if (exception == EXERROR && spclbltin <= 0) {
-				FORCEINTON;
-				break;
-			}
+		if (evalbltin(cmdentry.u.cmd, argc, argv, flags) &&
+		    !(exception == EXERROR && spclbltin <= 0)) {
 raise:
 			longjmp(handler->loc, 1);
 		}
@@ -892,6 +887,7 @@  raise:
 	}
 
 	status = waitforjob(jp);
+	FORCEINTON;
 
 out:
 	if (cmd->ncmd.redirect)
diff --git a/src/jobs.c b/src/jobs.c
index 1a97c54..606d603 100644
--- a/src/jobs.c
+++ b/src/jobs.c
@@ -975,10 +975,17 @@  waitforjob(struct job *jp)
 	int st;
 
 	TRACE(("waitforjob(%%%d) called\n", jp ? jobno(jp) : 0));
-	while ((jp && jp->state == JOBRUNNING) || gotsigchld)
-		dowait(DOWAIT_BLOCK, jp);
-	if (!jp)
+	if (!jp) {
+		int pid = gotsigchld;
+
+		while (pid > 0)
+			pid = dowait(DOWAIT_NORMAL, NULL);
+
 		return exitstatus;
+	}
+
+	while (jp->state == JOBRUNNING)
+		dowait(DOWAIT_BLOCK, jp);
 	st = getstatus(jp);
 #if JOBS
 	if (jp->jobctl) {