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, 5 insertions, 3 deletions

diff --git a/sys/kern/imgact_aout.c b/sys/kern/imgact_aout.c
index 4cb7b63..6bad705 100644
--- a/sys/kern/imgact_aout.c
+++ b/sys/kern/imgact_aout.c
@@ -177,14 +177,16 @@ exec_aout_imgact(imgp)
 	/*
 	 * text/data/bss must not exceed limits
 	 */
-	mtx_assert(&Giant, MA_OWNED);
+	PROC_LOCK(imgp->proc);
 	if (/* text can't exceed maximum text size */
 	    a_out->a_text > maxtsiz ||
 
 	    /* data + bss can't exceed rlimit */
-	    a_out->a_data + bss_size >
-		imgp->proc->p_rlimit[RLIMIT_DATA].rlim_cur)
+	    a_out->a_data + bss_size > lim_cur(imgp->proc, RLIMIT_DATA)) {
+			PROC_UNLOCK(imgp->proc);
 			return (ENOMEM);
+	}
+	PROC_UNLOCK(imgp->proc);
 
 	/* copy in arguments and/or environment from old process */
 	error = exec_extract_strings(imgp);