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, 20 insertions, 2 deletions

diff --git a/sys/sys/resourcevar.h b/sys/sys/resourcevar.h
index 5007c77..de04412 100644
--- a/sys/sys/resourcevar.h
+++ b/sys/sys/resourcevar.h
@@ -75,12 +75,23 @@ struct pstats {
  */
 struct plimit {
 	struct	rlimit pl_rlimit[RLIM_NLIMITS];
-	int	p_refcnt;		/* number of references */
+	int	pl_refcnt;		/* number of references */
+	struct	mtx pl_mtx;
 };
 
 #ifdef _KERNEL
 
 /*
+ * Lock order for operations involving the plimit lock:
+ *      filedesc  <important to avoid deadlocks in the descriptor code>
+ *      proc
+ *      plimit
+ */
+#define LIM_LOCK(lim)		mtx_lock(&(lim)->pl_mtx)
+#define LIM_UNLOCK(lim)		mtx_unlock(&(lim)->pl_mtx)
+#define LIM_LOCK_ASSERT(lim, f)	mtx_assert(&(lim)->pl_mtx, (f))
+
+/*
  * Per uid resource consumption
  */
 struct uidinfo {
@@ -107,8 +118,15 @@ int	 chgproccnt(struct uidinfo *uip, int diff, int max);
 int	 chgsbsize(struct uidinfo *uip, u_int *hiwat, u_int to,
 	    rlim_t max);
 int	 fuswintr(void *base);
+rlim_t	 lim_cur(struct proc *p, int which);
+rlim_t	 lim_max(struct proc *p, int which);
+void	 lim_rlimit(struct proc *p, int which, struct rlimit *rlp);
+void	 lim_copy(struct plimit *dst, struct plimit *src);
+void	 lim_free(struct plimit *limp);
+struct plimit
+	*lim_alloc(void);
 struct plimit
-	*limcopy(struct plimit *lim);
+	*lim_hold(struct plimit *limp);
 void	 ruadd(struct rusage *ru, struct rusage *ru2);
 int	 suswintr(void *base, int word);
 struct uidinfo