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, 2 deletions

diff --git a/sys/kern/uipc_sockbuf.c b/sys/kern/uipc_sockbuf.c
index 64199fc..9f5da29 100644
--- a/sys/kern/uipc_sockbuf.c
+++ b/sys/kern/uipc_sockbuf.c
@@ -411,6 +411,7 @@ sbreserve(sb, cc, so, td)
 	struct socket *so;
 	struct thread *td;
 {
+	rlim_t sbsize_limit;
 
 	/*
 	 * td will only be NULL when we're in an interrupt
@@ -418,10 +419,15 @@ sbreserve(sb, cc, so, td)
 	 */
 	if (cc > sb_max_adj)
 		return (0);
+	if (td != NULL) {
+		PROC_LOCK(td->td_proc);
+		sbsize_limit = lim_cur(td->td_proc, RLIMIT_SBSIZE);
+		PROC_UNLOCK(td->td_proc);
+	} else
+		sbsize_limit = RLIM_INFINITY;
 	if (!chgsbsize(so->so_cred->cr_uidinfo, &sb->sb_hiwat, cc,
-	    td ? td->td_proc->p_rlimit[RLIMIT_SBSIZE].rlim_cur : RLIM_INFINITY)) {
+	    sbsize_limit))
 		return (0);
-	}
 	sb->sb_mbmax = min(cc * sb_efficiency, sb_max);
 	if (sb->sb_lowat > sb->sb_hiwat)
 		sb->sb_lowat = sb->sb_hiwat;