Locking for the per-process resource limits structure.

- struct plimit includes a mutex to protect a reference count.  The plimit
  structure is treated similarly to struct ucred in that is is always copy
  on write, so having a reference to a structure is sufficient to read from
  it without needing a further lock.
- The proc lock protects the p_limit pointer and must be held while reading
  limits from a process to keep the limit structure from changing out from
  under you while reading from it.
- Various global limits that are ints are not protected by a lock since
  int writes are atomic on all the archs we support and thus a lock
  wouldn't buy us anything.
- All accesses to individual resource limits from a process are abstracted
  behind a simple lim_rlimit(), lim_max(), and lim_cur() API that return
  either an rlimit, or the current or max individual limit of the specified
  resource from a process.
- dosetrlimit() was renamed to kern_setrlimit() to match existing style of
  other similar syscall helper functions.
- The alpha OSF/1 compat layer no longer calls getrlimit() and setrlimit()
  (it didn't used the stackgap when it should have) but uses lim_rlimit()
  and kern_setrlimit() instead.
- The svr4 compat no longer uses the stackgap for resource limits calls,
  but uses lim_rlimit() and kern_setrlimit() instead.
- The ibcs2 compat no longer uses the stackgap for resource limits.  It
  also no longer uses the stackgap for accessing sysctl's for the
  ibcs2_sysconf() syscall but uses kernel_sysctl() instead.  As a result,
  ibcs2_sysconf() no longer needs Giant.
- The p_rlimit macro no longer exists.

Submitted by:	mtm (mostly, I only did a few cleanups and catchups)
Tested on:	i386
Compiled on:	alpha, amd64

1 files changed, 18 insertions, 4 deletions

diff --git a/sys/fs/procfs/procfs_rlimit.c b/sys/fs/procfs/procfs_rlimit.c
index 396c079..a9bb64d 100644
--- a/sys/fs/procfs/procfs_rlimit.c
+++ b/sys/fs/procfs/procfs_rlimit.c
@@ -46,11 +46,15 @@
 #define _RLIMIT_IDENT
 
 #include <sys/param.h>
+#include <sys/lock.h>
+#include <sys/mutex.h>
 #include <sys/systm.h>
 #include <sys/proc.h>
 #include <sys/resourcevar.h>
 #include <sys/resource.h>
 #include <sys/sbuf.h>
+#include <sys/types.h>
+#include <sys/malloc.h>
 
 #include <fs/pseudofs/pseudofs.h>
 #include <fs/procfs/procfs.h>
@@ -59,8 +63,17 @@
 int
 procfs_doprocrlimit(PFS_FILL_ARGS)
 {
+	struct plimit *limp;
 	int i;
 
+	/*
+	 * Obtain a private reference to resource limits
+	 */
+
+	PROC_LOCK(p);
+	limp = lim_hold(p->p_limit);
+	PROC_UNLOCK(p);
+
 	for (i = 0; i < RLIM_NLIMITS; i++) {
 
 		/*
@@ -77,24 +90,25 @@ procfs_doprocrlimit(PFS_FILL_ARGS)
 		 * current limit
 		 */
 
-		if (p->p_rlimit[i].rlim_cur == RLIM_INFINITY) {
+		if (limp->pl_rlimit[i].rlim_cur == RLIM_INFINITY) {
 			sbuf_printf(sb, "-1 ");
 		} else {
 			sbuf_printf(sb, "%llu ",
-				(unsigned long long)p->p_rlimit[i].rlim_cur);
+			    (unsigned long long)limp->pl_rlimit[i].rlim_cur);
 		}
 
 		/*
 		 * maximum limit
 		 */
 
-		if (p->p_rlimit[i].rlim_max == RLIM_INFINITY) {
+		if (limp->pl_rlimit[i].rlim_max == RLIM_INFINITY) {
 			sbuf_printf(sb, "-1\n");
 		} else {
 			sbuf_printf(sb, "%llu\n",
-				(unsigned long long)p->p_rlimit[i].rlim_max);
+			    (unsigned long long)limp->pl_rlimit[i].rlim_max);
 		}
 	}
 
+	lim_free(limp);
 	return (0);
 }