Add a per-thread ucred reference for syscalls and synchronous traps from

userland.  The per thread ucred reference is immutable and thus needs no
locks to be read.  However, until all the proc locking associated with
writes to p_ucred are completed, it is still not safe to use the per-thread
reference.

Tested on:	x86 (SMP), alpha, sparc64

1 files changed, 37 insertions, 26 deletions

diff --git a/sys/i386/i386/trap.c b/sys/i386/i386/trap.c
index fd4c8fe..714f3f2 100644
--- a/sys/i386/i386/trap.c
+++ b/sys/i386/i386/trap.c
@@ -216,6 +216,17 @@ trap(frame)
 	eva = 0;
 	type = frame.tf_trapno;
 	code = frame.tf_err;
+	if (type == T_PAGEFLT) {
+		/*
+		 * For some Cyrix CPUs, %cr2 is clobbered by
+		 * interrupts.  This problem is worked around by using
+		 * an interrupt gate for the pagefault handler.  We
+		 * are finally ready to read %cr2 and then must
+		 * reenable interrupts.
+		 */
+		eva = rcr2();
+		enable_intr();
+	}
 
         if ((ISPL(frame.tf_cs) == SEL_UPL) ||
 	    ((frame.tf_eflags & PSL_VM) && !in_vm86call)) {
@@ -223,6 +234,10 @@ trap(frame)
 
 		sticks = td->td_kse->ke_sticks;
 		td->td_frame = &frame;
+		KASSERT(td->td_ucred == NULL, ("already have a ucred"));
+		PROC_LOCK(p);
+		td->td_ucred = crhold(p->p_ucred);
+		PROC_UNLOCK(p);
 
 		switch (type) {
 		case T_PRIVINFLT:	/* privileged instruction fault */
@@ -240,7 +255,7 @@ trap(frame)
 #ifdef DEV_NPX
 			ucode = npxtrap();
 			if (ucode == -1)
-				return;
+				goto userout;
 #else
 			ucode = code;
 #endif
@@ -273,15 +288,6 @@ trap(frame)
 			break;
 
 		case T_PAGEFLT:		/* page fault */
-			/*
-			 * For some Cyrix CPUs, %cr2 is clobbered by
-			 * interrupts.  This problem is worked around by using
-			 * an interrupt gate for the pagefault handler.  We
-			 * are finally ready to read %cr2 and then must
-			 * reenable interrupts.
-			 */
-			eva = rcr2();
-			enable_intr();
 			i = trap_pfault(&frame, TRUE, eva);
 #if defined(I586_CPU) && !defined(NO_F00F_HACK)
 			if (i == -2) {
@@ -299,7 +305,7 @@ trap(frame)
 			}
 #endif
 			if (i == -1)
-				goto out;
+				goto userout;
 			if (i == 0)
 				goto user;
 
@@ -324,7 +330,7 @@ trap(frame)
 				lastalert = time_second;
 			}
 			mtx_unlock(&Giant);
-			goto out;
+			goto userout;
 #else /* !POWERFAIL_NMI */
 			/* machine/parity/power fail/"kitchen sink" faults */
 			/* XXX Giant */
@@ -339,7 +345,7 @@ trap(frame)
 					kdb_trap (type, 0, &frame);
 				}
 #endif /* DDB */
-				goto out;
+				goto userout;
 			} else if (panic_on_nmi)
 				panic("NMI indicates hardware failure");
 			break;
@@ -360,7 +366,7 @@ trap(frame)
 #ifdef DEV_NPX
 			/* transparent fault (due to context switch "late") */
 			if (npxdna())
-				goto out;
+				goto userout;
 #endif
 			if (!pmath_emulate) {
 				i = SIGFPE;
@@ -372,7 +378,7 @@ trap(frame)
 			mtx_unlock(&Giant);
 			if (i == 0) {
 				if (!(frame.tf_eflags & PSL_T))
-					goto out;
+					goto userout;
 				frame.tf_eflags &= ~PSL_T;
 				i = SIGTRAP;
 			}
@@ -392,17 +398,10 @@ trap(frame)
 	} else {
 		/* kernel trap */
 
+		KASSERT(cold || td->td_ucred != NULL,
+		    ("kernel trap doesn't have ucred"));
 		switch (type) {
 		case T_PAGEFLT:			/* page fault */
-			/*
-			 * For some Cyrix CPUs, %cr2 is clobbered by
-			 * interrupts.  This problem is worked around by using
-			 * an interrupt gate for the pagefault handler.  We
-			 * are finally ready to read %cr2 and then must
-			 * reenable interrupts.
-			 */
-			eva = rcr2();
-			enable_intr();
 			(void) trap_pfault(&frame, FALSE, eva);
 			goto out;
 
@@ -622,8 +621,12 @@ trap(frame)
 
 user:
 	userret(td, &frame, sticks);
-	if (mtx_owned(&Giant))	/* XXX why would Giant be owned here? */
-		mtx_unlock(&Giant);
+	mtx_assert(&Giant, MA_NOTOWNED);
+userout:
+	mtx_lock(&Giant);
+	crfree(td->td_ucred);
+	mtx_unlock(&Giant);
+	td->td_ucred = NULL;
 out:
 	return;
 }
@@ -1046,6 +1049,10 @@ syscall(frame)
 
 	sticks = td->td_kse->ke_sticks;
 	td->td_frame = &frame;
+	KASSERT(td->td_ucred == NULL, ("already have a ucred"));
+	PROC_LOCK(p);
+	td->td_ucred = crhold(p->p_ucred);
+	PROC_UNLOCK(p);
 	params = (caddr_t)frame.tf_esp + sizeof(int);
 	code = frame.tf_eax;
 
@@ -1187,6 +1194,10 @@ bad:
 	 */
 	STOPEVENT(p, S_SCX, code);
 
+	mtx_lock(&Giant);
+	crfree(td->td_ucred);
+	mtx_unlock(&Giant);
+	td->td_ucred = NULL;
 #ifdef WITNESS
 	if (witness_list(td)) {
 		panic("system call %s returning with mutex(s) held\n",