[master] b845c2789 Retire the kill(SIGNULL) test in VSM

[Martin Blix Grydeland]

commit b845c2789cae4f165e30a3d0f3af1bfbbeca98ee
Author: Martin Blix Grydeland <martin at varnish-software.com>
Date:   Tue Sep 10 16:31:04 2019 +0200

    Retire the kill(SIGNULL) test in VSM
    
    A bug was uncovered in the VSM code that checks if kill(SIGNULL) would
    work as a test of liveness of the master and worker processes. If the user
    running the utility has the required permissions to send signal to the
    worker process, but not the management process, the code would wrongly
    assume it could do kill on both. It would then end up in a connect loop
    never succeeding.
    
    Because kill() can not always be successfully run (a common scenario when
    the user running varnishlog is not the same UID as the cache processes),
    there is a fall back to using fstat to check for Varnish restarts. Since
    this fallback is active for most use cases anyways, it was decided to
    retire the kill() mechanism rather than to fix it. This way the behaviour
    does not change depending on what user the utility is run as.
    
    This change was OK'd by PHK after discussing it on IRC.

diff --git a/bin/varnishtest/tests/u00008.vtc b/bin/varnishtest/tests/u00008.vtc
index 0c35fb3fc..9953fccad 100644
--- a/bin/varnishtest/tests/u00008.vtc
+++ b/bin/varnishtest/tests/u00008.vtc
@@ -37,10 +37,6 @@ process p1 -expect-text 0 0 "VBE.vcl1.s1.req"
 process p1 -expect-text 0 0 "DIAG"
 process p1 -screen_dump
 
-varnish v1 -stop
-process p1 -expect-text 2 1 "Uptime child:   Not Running"
-process p1 -screen_dump
-
 process p1 -write {dek}
 process p1 -expect-text 0 1 "Concurrent connections to backend:"
 process p1 -screen_dump
diff --git a/lib/libvarnishapi/vsm.c b/lib/libvarnishapi/vsm.c
index 91540c8fd..31bc6f023 100644
--- a/lib/libvarnishapi/vsm.c
+++ b/lib/libvarnishapi/vsm.c
@@ -150,8 +150,6 @@ struct vsm {
 
 	int			attached;
 	double			patience;
-
-	int			couldkill;
 };
 
 /*--------------------------------------------------------------------*/
@@ -357,8 +355,6 @@ VSM_New(void)
 	vd->child->vsm = vd;
 	vd->wdfd = -1;
 	vd->patience = 5;
-	if (getenv("VSM_NOPID") != NULL)
-		vd->couldkill = -1;
 	return (vd);
 }
 
@@ -485,17 +481,13 @@ vsm_vlu_hash(struct vsm *vd, struct vsm_set *vs, const char *line)
 	int i;
 	uintmax_t id1, id2;
 
+	(void)vd;
+
 	i = sscanf(line, "# %ju %ju", &id1, &id2);
 	if (i != 2) {
 		vs->retval |= VSM_MGT_RESTARTED | VSM_MGT_CHANGED;
 		return (0);
 	}
-	if (vd->couldkill >= 0 && !kill(id1, 0)) {
-		vd->couldkill = 1;
-	} else if (vd->couldkill > 0 && errno == ESRCH) {
-		vs->retval |= VSM_MGT_RESTARTED | VSM_MGT_CHANGED;
-		return (0);
-	}
 	vs->retval |= VSM_MGT_RUNNING;
 	if (id1 != vs->id1 || id2 != vs->id2) {
 		vs->retval |= VSM_MGT_RESTARTED | VSM_MGT_CHANGED;
@@ -694,8 +686,7 @@ vsm_refresh_set(struct vsm *vd, struct vsm_set *vs)
 
 	vs->fst.st_size = lseek(vs->fd, 0L, SEEK_CUR);
 
-	if (vd->couldkill < 1 || !kill(vs->id1, 0))
-		vs->retval |= vs->flag_running;
+	vs->retval |= vs->flag_running;
 	return (vs->retval);
 }