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, 9 insertions, 5 deletions

diff --git a/sys/kern/kern_acct.c b/sys/kern/kern_acct.c
index 827a034..613a198 100644
--- a/sys/kern/kern_acct.c
+++ b/sys/kern/kern_acct.c
@@ -228,6 +228,7 @@ acct_process(td)
 	int t, ret;
 	struct vnode *vp;
 	struct ucred *uc;
+	struct plimit *newlim, *oldlim;
 
 	mtx_lock(&acct_mtx);
 
@@ -300,11 +301,14 @@ acct_process(td)
 	/*
 	 * Eliminate any file size rlimit.
 	 */
-	if (p->p_limit->p_refcnt > 1) {
-		p->p_limit->p_refcnt--;
-		p->p_limit = limcopy(p->p_limit);
-	}
-	p->p_rlimit[RLIMIT_FSIZE].rlim_cur = RLIM_INFINITY;
+	newlim = lim_alloc();
+	PROC_LOCK(p);
+	oldlim = p->p_limit;
+	lim_copy(newlim, oldlim);
+	newlim->pl_rlimit[RLIMIT_FSIZE].rlim_cur = RLIM_INFINITY;
+	p->p_limit = newlim;
+	PROC_UNLOCK(p);
+	lim_free(oldlim);
 
 	VOP_LEASE(vp, td, uc, LEASE_WRITE);
 	ret = vn_rdwr(UIO_WRITE, vp, (caddr_t)&acct, sizeof (acct),