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, 16 insertions, 7 deletions

diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
index b6eaee271a6c..abaac90655e6 100644
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -224,10 +224,10 @@ getdtablesize(td, uap)
 {
 	struct proc *p = td->td_proc;
 
-	mtx_lock(&Giant);
+	PROC_LOCK(p);
 	td->td_retval[0] =
-	    min((int)p->p_rlimit[RLIMIT_NOFILE].rlim_cur, maxfilesperproc);
-	mtx_unlock(&Giant);
+	    min((int)lim_cur(p, RLIMIT_NOFILE), maxfilesperproc);
+	PROC_UNLOCK(p);
 	return (0);
 }
 
@@ -353,11 +353,14 @@ kern_fcntl(struct thread *td, int fd, int cmd, intptr_t arg)
 	case F_DUPFD:
 		FILEDESC_UNLOCK(fdp);
 		newmin = arg;
-		if (newmin >= p->p_rlimit[RLIMIT_NOFILE].rlim_cur ||
+		PROC_LOCK(p);
+		if (newmin >= lim_cur(p, RLIMIT_NOFILE) ||
 		    newmin >= maxfilesperproc) {
+			PROC_UNLOCK(p);
 			error = EINVAL;
 			break;
 		}
+		PROC_UNLOCK(p);
 		error = do_dup(td, DUP_VARIABLE, fd, newmin, td->td_retval);
 		break;
 
@@ -572,7 +575,9 @@ do_dup(td, type, old, new, retval)
 	 */
 	if (old < 0 || new < 0)
 		return (EBADF);
-	maxfd = min((int)p->p_rlimit[RLIMIT_NOFILE].rlim_cur, maxfilesperproc);
+	PROC_LOCK(p);
+	maxfd = min((int)lim_cur(p, RLIMIT_NOFILE), maxfilesperproc);
+	PROC_UNLOCK(p);
 	if (new >= maxfd)
 		return (EMFILE);
 
@@ -1213,7 +1218,9 @@ fdalloc(struct thread *td, int minfd, int *result)
 
 	FILEDESC_LOCK_ASSERT(fdp, MA_OWNED);
 
-	maxfd = min((int)p->p_rlimit[RLIMIT_NOFILE].rlim_cur, maxfilesperproc);
+	PROC_LOCK(p);
+	maxfd = min((int)lim_cur(p, RLIMIT_NOFILE), maxfilesperproc);
+	PROC_UNLOCK(p);
 
 	/*
 	 * Search the bitmap for a free descriptor.  If none is found, try
@@ -1261,7 +1268,9 @@ fdavail(td, n)
 
 	FILEDESC_LOCK_ASSERT(fdp, MA_OWNED);
 
-	lim = min((int)p->p_rlimit[RLIMIT_NOFILE].rlim_cur, maxfilesperproc);
+	PROC_LOCK(p);
+	lim = min((int)lim_cur(p, RLIMIT_NOFILE), maxfilesperproc);
+	PROC_UNLOCK(p);
 	if ((i = lim - fdp->fd_nfiles) > 0 && (n -= i) <= 0)
 		return (1);
 	last = min(fdp->fd_nfiles, lim);