From 2eb927e2bb836a41f794d8a3887c4c6d438bcb90 Mon Sep 17 00:00:00 2001
From: Julian Elischer <julian@FreeBSD.org>
Date: Sun, 17 Feb 2002 01:09:56 +0000
Subject: [PATCH] If the credential on an incoming thread is correct, don't
 bother reaquiring it. In the same vein, don't bother dropping the thread cred
 when goinf ot userland. We are guaranteed to nned it when we come back,
 (which we are guaranteed to do).

Reviewed by:	jhb@freebsd.org, bde@freebsd.org (slightly different version)
---
 sys/amd64/amd64/trap.c | 14 ++++++++------
 sys/i386/i386/trap.c   | 14 ++++++++------
 sys/kern/kern_fork.c   |  2 ++
 sys/kern/kern_prot.c   | 21 +++++++++++++++++++++
 sys/kern/subr_trap.c   |  7 ++++---
 sys/sys/ucred.h        |  1 +
 6 files changed, 44 insertions(+), 15 deletions(-)

diff --git a/sys/amd64/amd64/trap.c b/sys/amd64/amd64/trap.c
index 07067c407b3f..bc31c8ce21ec 100644
--- a/sys/amd64/amd64/trap.c
+++ b/sys/amd64/amd64/trap.c
@@ -256,9 +256,8 @@ 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);
+		if (td->td_ucred != p->p_ucred) 
+			cred_update_thread(td);
 
 		switch (type) {
 		case T_PRIVINFLT:	/* privileged instruction fault */
@@ -644,10 +643,12 @@ trap(frame)
 	userret(td, &frame, sticks);
 	mtx_assert(&Giant, MA_NOTOWNED);
 userout:
+#ifdef	INVARIANTS
 	mtx_lock(&Giant);
 	crfree(td->td_ucred);
 	mtx_unlock(&Giant);
 	td->td_ucred = NULL;
+#endif
 out:
 	return;
 }
@@ -954,9 +955,8 @@ 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);
+	if (td->td_ucred != p->p_ucred) 
+		cred_update_thread(td);
 	params = (caddr_t)frame.tf_esp + sizeof(int);
 	code = frame.tf_eax;
 	orig_tf_eflags = frame.tf_eflags;
@@ -1099,10 +1099,12 @@ syscall(frame)
 	 */
 	STOPEVENT(p, S_SCX, code);
 
+#ifdef	INVARIANTS
 	mtx_lock(&Giant);
 	crfree(td->td_ucred);
 	mtx_unlock(&Giant);
 	td->td_ucred = NULL;
+#endif
 #ifdef WITNESS
 	if (witness_list(td)) {
 		panic("system call %s returning with mutex(s) held\n",
diff --git a/sys/i386/i386/trap.c b/sys/i386/i386/trap.c
index 07067c407b3f..bc31c8ce21ec 100644
--- a/sys/i386/i386/trap.c
+++ b/sys/i386/i386/trap.c
@@ -256,9 +256,8 @@ 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);
+		if (td->td_ucred != p->p_ucred) 
+			cred_update_thread(td);
 
 		switch (type) {
 		case T_PRIVINFLT:	/* privileged instruction fault */
@@ -644,10 +643,12 @@ trap(frame)
 	userret(td, &frame, sticks);
 	mtx_assert(&Giant, MA_NOTOWNED);
 userout:
+#ifdef	INVARIANTS
 	mtx_lock(&Giant);
 	crfree(td->td_ucred);
 	mtx_unlock(&Giant);
 	td->td_ucred = NULL;
+#endif
 out:
 	return;
 }
@@ -954,9 +955,8 @@ 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);
+	if (td->td_ucred != p->p_ucred) 
+		cred_update_thread(td);
 	params = (caddr_t)frame.tf_esp + sizeof(int);
 	code = frame.tf_eax;
 	orig_tf_eflags = frame.tf_eflags;
@@ -1099,10 +1099,12 @@ syscall(frame)
 	 */
 	STOPEVENT(p, S_SCX, code);
 
+#ifdef	INVARIANTS
 	mtx_lock(&Giant);
 	crfree(td->td_ucred);
 	mtx_unlock(&Giant);
 	td->td_ucred = NULL;
+#endif
 #ifdef WITNESS
 	if (witness_list(td)) {
 		panic("system call %s returning with mutex(s) held\n",
diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c
index 3223f8b55386..c7cbf2808543 100644
--- a/sys/kern/kern_fork.c
+++ b/sys/kern/kern_fork.c
@@ -799,10 +799,12 @@ fork_exit(callout, arg, frame)
 		kthread_exit(0);
 	}
 	PROC_UNLOCK(p);
+#ifdef	INVARIANTS
 	mtx_lock(&Giant);
 	crfree(td->td_ucred);
 	mtx_unlock(&Giant);
 	td->td_ucred = NULL;
+#endif
 	mtx_assert(&Giant, MA_NOTOWNED);
 }
 
diff --git a/sys/kern/kern_prot.c b/sys/kern/kern_prot.c
index 4214cc1ddf40..f7056a0eca53 100644
--- a/sys/kern/kern_prot.c
+++ b/sys/kern/kern_prot.c
@@ -1683,6 +1683,27 @@ crdup(cr)
 	return (newcr);
 }
 
+/*
+ * small routine to swap a thread's current ucred for the correct one
+ * taken from the process.
+ */
+void
+cred_update_thread(struct thread *td)
+{
+	struct proc *p;
+
+	p = td->td_proc;
+	if (td->td_ucred != NULL) {
+		mtx_lock(&Giant);
+		crfree(td->td_ucred);
+		mtx_unlock(&Giant);
+		td->td_ucred = NULL;
+	}
+	PROC_LOCK(p);
+	td->td_ucred = crhold(p->p_ucred);
+	PROC_UNLOCK(p);
+}
+
 /*
  * Get login name, if available.
  */
diff --git a/sys/kern/subr_trap.c b/sys/kern/subr_trap.c
index 9c24e172215c..d599b91bfa23 100644
--- a/sys/kern/subr_trap.c
+++ b/sys/kern/subr_trap.c
@@ -161,9 +161,8 @@ ast(framep)
 			p->p_stats->p_prof.pr_ticks = 0;
 		}
 		mtx_unlock_spin(&sched_lock);
-		PROC_LOCK(p);
-		td->td_ucred = crhold(p->p_ucred);
-		PROC_UNLOCK(p);
+		if (td->td_ucred != p->p_ucred) 
+			cred_update_thread(td);
 		if (flags & KEF_OWEUPC && sflag & PS_PROFIL)
 			addupc_task(ke, p->p_stats->p_prof.pr_addr, prticks);
 		if (sflag & PS_ALRMPEND) {
@@ -188,10 +187,12 @@ ast(framep)
 		}
 
 		userret(td, framep, sticks);
+#ifdef	INVARIANTS
 		mtx_lock(&Giant);
 		crfree(td->td_ucred);
 		mtx_unlock(&Giant);
 		td->td_ucred = NULL;
+#endif
 		s = cpu_critical_enter();
 	}
 	mtx_assert(&Giant, MA_NOTOWNED);
diff --git a/sys/sys/ucred.h b/sys/sys/ucred.h
index d92b45deafdc..d26f3183fe84 100644
--- a/sys/sys/ucred.h
+++ b/sys/sys/ucred.h
@@ -83,6 +83,7 @@ struct xucred {
 #ifdef _KERNEL
 
 
+void		cred_update_thread(struct thread *td);
 void		change_egid (struct ucred *newcred, gid_t egid);
 void		change_euid (struct ucred *newcred, uid_t euid);
 void		change_rgid (struct ucred *newcred, gid_t rgid);