Add some DIAGNOSTIC code.

While in userland, keep the thread's ucred reference in a shadow
field so that the usual place to store it is NULL.
If DIAGNOSTIC is not set, the thread ucred is kept valid until the next
kernel entry, at which time it is checked against the process cred
and possibly corrected. Produces a BIG speedup in
kernels with INVARIANTS set. (A previous commit corrected it
for the non INVARIANTS case already)

Reviewed by:	dillon@freebsd.org

1 files changed, 22 insertions, 12 deletions

diff --git a/sys/alpha/alpha/trap.c b/sys/alpha/alpha/trap.c
index 2cdf540d..c0b1327 100644
--- a/sys/alpha/alpha/trap.c
+++ b/sys/alpha/alpha/trap.c
@@ -297,7 +297,12 @@ trap(a0, a1, a2, entry, framep)
 	if (user)  {
 		sticks = td->td_kse->ke_sticks;
 		td->td_frame = framep;
-		KASSERT(td->td_ucred == NULL, ("already have a ucred"));
+#ifdef DIAGNOSTIC 			/* see the comment in ast() */
+		if (td->td_ucred)
+			panic("trap: thread got a cred while in userspace");
+		td->td_ucred = td->td_ucred_cache;
+		td->td_ucred_cache = NULL;
+#endif /* DIAGNOSTIC */
 		if (td->td_ucred != p->p_ucred)
 			cred_update_thread(td);
 	} else {
@@ -625,12 +630,12 @@ out:
 		framep->tf_regs[FRAME_SP] = alpha_pal_rdusp();
 		userret(td, framep, sticks);
 		mtx_assert(&Giant, MA_NOTOWNED);
-#ifdef	INVARIANTS
-		mtx_lock(&Giant);
-		crfree(td->td_ucred);
-		mtx_unlock(&Giant);
+#ifdef DIAGNOSTIC 			/* see the comment in ast() */
+		if (td->td_ucred_cache)
+			panic("trap: thread already has cached ucred");
+		td->td_ucred_cache = td->td_ucred;
 		td->td_ucred = NULL;
-#endif
+#endif /* DIAGNOSTIC */
 	}
 	return;
 
@@ -699,7 +704,12 @@ syscall(code, framep)
 	td->td_frame = framep;
 	opc = framep->tf_regs[FRAME_PC] - 4;
 	sticks = td->td_kse->ke_sticks;
-	KASSERT(td->td_ucred == NULL, ("already have a ucred"));
+#ifdef DIAGNOSTIC 			/* see the comment in ast() */
+	if (td->td_ucred)
+		panic("syscall:thread got a cred while in userspace");
+	td->td_ucred = td->td_ucred_cache;
+	td->td_ucred_cache = NULL;
+#endif /* DIAGNOSTIC */
 	if (td->td_ucred != p->p_ucred)
 		cred_update_thread(td);
 
@@ -822,12 +832,12 @@ syscall(code, framep)
 	 */
 	STOPEVENT(p, S_SCX, code);
 
-#ifdef	INVARIANTS
-	mtx_lock(&Giant);
-	crfree(td->td_ucred);
-	mtx_unlock(&Giant);
+#ifdef DIAGNOSTIC 			/* see the comment in ast() */
+	if (td->td_ucred_cache)
+		panic("syscall:thread already has cached ucred");
+	td->td_ucred_cache = td->td_ucred;
 	td->td_ucred = NULL;
-#endif
+#endif /* DIAGNOSTIC */
 #ifdef WITNESS
 	if (witness_list(td)) {
 		panic("system call %s returning with mutex(s) held\n",