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, 3 insertions, 2 deletions

diff --git a/sys/vm/vm_pageout.c b/sys/vm/vm_pageout.c
index 471f9b3..506f1ec 100644
--- a/sys/vm/vm_pageout.c
+++ b/sys/vm/vm_pageout.c
@@ -1486,6 +1486,7 @@ vm_daemon()
 	struct proc *p;
 	int breakout;
 	struct thread *td;
+	struct rlimit rsslim;
 
 	mtx_lock(&Giant);
 	while (TRUE) {
@@ -1511,6 +1512,7 @@ vm_daemon()
 				PROC_UNLOCK(p);
 				continue;
 			}
+			lim_rlimit(p, RLIMIT_RSS, &rsslim);
 			/*
 			 * if the process is in a non-running type state,
 			 * don't touch it.
@@ -1534,8 +1536,7 @@ vm_daemon()
 			 * get a limit
 			 */
 			limit = OFF_TO_IDX(
-			    qmin(p->p_rlimit[RLIMIT_RSS].rlim_cur,
-				p->p_rlimit[RLIMIT_RSS].rlim_max));
+			    qmin(rsslim.rlim_cur, rsslim.rlim_max));
 
 			/*
 			 * let processes that are swapped out really be