Module Name: src
Committed By: kamil
Date: Tue Mar 13 02:24:26 UTC 2018
Modified Files:
src/sys/kern: kern_proc.c
Log Message:
Make sysctl_doeproc() more predictable
Swap the order of looking into zombie and all process lists, start now
with the zombie one. This prevents a race observed previously that the
same process could be detected on both lists during a single polling call.
While there:
- Short-circuit break for KERN_PROC_PID, once a pid has been detected.
- Removal of redundant "if (kbuf)" and "if (marker)" checks.
- Update of comments regarding potential optimization, explaining why we
don't want to it as of now. Performance gain from lookup call vs
iteration over a list is neglible on a regular system.
- Return ESRCH when no results have been found. This allows more easily
to implement a retry or abandon algorithm.
This corrects races observed in the existing ATF ptrace(2) tests, related
to await_zombie(). This function was expecting to check whether a process
has been transformed into a zombie, however it was causing occasional
crashes as it was overflowing the return buffer, returning the same pid
twice: once from allproc list and the second time from zombieproc one.
Fix suggested by <christos>
Short-circuit break suggested by <kre>
Discussed on tech-kern.
Sponsored by <The NetBSD Foundation>
To generate a diff of this commit:
cvs rdiff -u -r1.210 -r1.211 src/sys/kern/kern_proc.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/kern_proc.c
diff -u src/sys/kern/kern_proc.c:1.210 src/sys/kern/kern_proc.c:1.211
--- src/sys/kern/kern_proc.c:1.210 Sun Mar 11 15:13:05 2018
+++ src/sys/kern/kern_proc.c Tue Mar 13 02:24:26 2018
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_proc.c,v 1.210 2018/03/11 15:13:05 kre Exp $ */
+/* $NetBSD: kern_proc.c,v 1.211 2018/03/13 02:24:26 kamil Exp $ */
/*-
* Copyright (c) 1999, 2006, 2007, 2008 The NetBSD Foundation, Inc.
@@ -62,7 +62,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_proc.c,v 1.210 2018/03/11 15:13:05 kre Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_proc.c,v 1.211 2018/03/13 02:24:26 kamil Exp $");
#ifdef _KERNEL_OPT
#include "opt_kstack.h"
@@ -1674,12 +1674,16 @@ sysctl_doeproc(SYSCTLFN_ARGS)
marker->p_flag = PK_MARKER;
mutex_enter(proc_lock);
- mmmbrains = false;
- for (p = LIST_FIRST(&allproc);; p = next) {
+ /*
+ * Start with zombies to prevent reporting processes twice, in case they
+ * are dying and being moved from the list of alive processes to zombies.
+ */
+ mmmbrains = true;
+ for (p = LIST_FIRST(&zombproc);; p = next) {
if (p == NULL) {
- if (!mmmbrains) {
- p = LIST_FIRST(&zombproc);
- mmmbrains = true;
+ if (mmmbrains) {
+ p = LIST_FIRST(&allproc);
+ mmmbrains = false;
}
if (p == NULL)
break;
@@ -1704,17 +1708,17 @@ sysctl_doeproc(SYSCTLFN_ARGS)
}
/*
- * TODO - make more efficient (see notes below).
- * do by session.
+ * Hande all the operations in one switch on the cost of
+ * algorithm complexity is on purpose. The win splitting this
+ * function into several similar copies makes maintenance burden
+ * burden, code grow and boost is neglible in practical systems.
*/
switch (op) {
case KERN_PROC_PID:
- /* could do this with just a lookup */
match = (p->p_pid == (pid_t)arg);
break;
case KERN_PROC_PGRP:
- /* could do this by traversing pgrp */
match = (p->p_pgrp->pg_id == (pid_t)arg);
break;
@@ -1820,10 +1824,20 @@ sysctl_doeproc(SYSCTLFN_ARGS)
rw_exit(&p->p_reflock);
next = LIST_NEXT(p, p_list);
}
+
+ /*
+ * Short-circuit break quickly!
+ */
+ if (op == KERN_PROC_PID)
+ break;
}
mutex_exit(proc_lock);
if (where != NULL) {
+ if (needed == 0) {
+ error = ESRCH;
+ goto out;
+ }
*oldlenp = dp - where;
if (needed > *oldlenp) {
error = ENOMEM;
@@ -1833,10 +1847,8 @@ sysctl_doeproc(SYSCTLFN_ARGS)
needed += KERN_PROCSLOP;
*oldlenp = needed;
}
- if (kbuf)
- kmem_free(kbuf, sizeof(*kbuf));
- if (marker)
- kmem_free(marker, sizeof(*marker));
+ kmem_free(kbuf, sizeof(*kbuf));
+ kmem_free(marker, sizeof(*marker));
sysctl_relock();
return 0;
bah:
@@ -1847,10 +1859,8 @@ sysctl_doeproc(SYSCTLFN_ARGS)
cleanup:
mutex_exit(proc_lock);
out:
- if (kbuf)
- kmem_free(kbuf, sizeof(*kbuf));
- if (marker)
- kmem_free(marker, sizeof(*marker));
+ kmem_free(kbuf, sizeof(*kbuf));
+ kmem_free(marker, sizeof(*marker));
sysctl_relock();
return error;
}
