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, 8 insertions, 4 deletions

diff --git a/sys/vm/vm_unix.c b/sys/vm/vm_unix.c
index 877609f1eb77..6313cc1125a0 100644
--- a/sys/vm/vm_unix.c
+++ b/sys/vm/vm_unix.c
@@ -77,10 +77,16 @@ obreak(td, uap)
 {
 	struct vmspace *vm = td->td_proc->p_vmspace;
 	vm_offset_t new, old, base;
+	rlim_t datalim, vmemlim;
 	int rv;
 	int error = 0;
 	boolean_t do_map_wirefuture;
 
+	PROC_LOCK(td->td_proc);
+	datalim = lim_cur(td->td_proc, RLIMIT_DATA);
+	vmemlim = lim_cur(td->td_proc, RLIMIT_VMEM);
+	PROC_UNLOCK(td->td_proc);
+
 	do_map_wirefuture = FALSE;
 	new = round_page((vm_offset_t)uap->nsize);
 	vm_map_lock(&vm->vm_map);
@@ -92,8 +98,7 @@ obreak(td, uap)
 		 * Check the resource limit, but allow a process to reduce
 		 * its usage, even if it remains over the limit.
 		 */
-		if (new - base > td->td_proc->p_rlimit[RLIMIT_DATA].rlim_cur &&
-		    new > old) {
+		if (new - base > datalim && new > old) {
 			error = ENOMEM;
 			goto done;
 		}
@@ -111,8 +116,7 @@ obreak(td, uap)
 		goto done;
 	}
 	if (new > old) {
-		if (vm->vm_map.size + (new - old) >
-		    td->td_proc->p_rlimit[RLIMIT_VMEM].rlim_cur) {
+		if (vm->vm_map.size + (new - old) > vmemlim) {
 			error = ENOMEM;
 			goto done;
 		}