From 08e732a88ba0d12d11fa8b38d5932c6579273aca Mon Sep 17 00:00:00 2001
From: dillon <dillon@FreeBSD.org>
Date: Thu, 30 Aug 2001 18:50:57 +0000
Subject: Remove the MPSAFE keyword from the parser for syscalls.master.
 Instead introduce the [M] prefix to existing keywords.  e.g. MSTD is the MP
 SAFE version of STD.  This is prepatory for a massive Giant lock pushdown. 
 The old MPSAFE keyword made syscalls.master too messy.

Begin comments MP-Safe procedures with the comment:
/*
 * MPSAFE
 */
This comments means that the procedure may be called without
Giant held (The procedure itself may still need to obtain
Giant temporarily to do its thing).

sv_prepsyscall() is now MP SAFE and assumed to be MP SAFE
sv_transtrap() is now MP SAFE and assumed to be MP SAFE

ktrsyscall() and ktrsysret() are now MP SAFE (Giant Pushdown)
trapsignal() is now MP SAFE (Giant Pushdown)

Places which used to do the if (mtx_owned(&Giant)) mtx_unlock(&Giant)
test in syscall[2]() in */*/trap.c now do not.  Instead they
explicitly unlock Giant if they previously obtained it, and then
assert that it is no longer held to catch broken system calls.

Rebuild syscall tables.
---
 sys/amd64/amd64/trap.c | 28 +++++++++++-----------------
 1 file changed, 11 insertions(+), 17 deletions(-)

(limited to 'sys/amd64')

diff --git a/sys/amd64/amd64/trap.c b/sys/amd64/amd64/trap.c
index 11effc3..4e72f9b 100644
--- a/sys/amd64/amd64/trap.c
+++ b/sys/amd64/amd64/trap.c
@@ -603,7 +603,6 @@ restart:
 		goto out;
 	}
 
-	mtx_lock(&Giant);
 	/* Translate fault for emulators (e.g. Linux) */
 	if (*p->p_sysent->sv_transtrap)
 		i = (*p->p_sysent->sv_transtrap)(i, type);
@@ -619,11 +618,10 @@ restart:
 		uprintf("\n");
 	}
 #endif
-	mtx_unlock(&Giant);
 
 user:
 	userret(p, &frame, sticks);
-	if (mtx_owned(&Giant))
+	if (mtx_owned(&Giant))	/* XXX why would Giant be owned here? */
 		mtx_unlock(&Giant);
 out:
 	return;
@@ -1034,9 +1032,10 @@ syscall(frame)
 
 #ifdef DIAGNOSTIC
 	if (ISPL(frame.tf_cs) != SEL_UPL) {
-		mtx_lock(&Giant);
+		mtx_lock(&Giant);	/* try to stabilize the system XXX */
 		panic("syscall");
 		/* NOT REACHED */
+		mtx_unlock(&Giant);
 	}
 #endif
 
@@ -1047,11 +1046,9 @@ syscall(frame)
 
 	if (p->p_sysent->sv_prepsyscall) {
 		/*
-		 * The prep code is not MP aware.
+		 * The prep code is MP aware.
 		 */
-		mtx_lock(&Giant);
 		(*p->p_sysent->sv_prepsyscall)(&frame, args, &code, &params);
-		mtx_unlock(&Giant);
 	} else {
 		/*
 		 * Need to check if this is a 32 bit or 64 bit syscall.
@@ -1084,11 +1081,10 @@ syscall(frame)
 	narg = callp->sy_narg & SYF_ARGMASK;
 
 	/*
-	 * copyin is MP aware, but the tracing code is not
+	 * copyin and the ktrsyscall()/ktrsysret() code is MP-aware
 	 */
 	if (params && (i = narg * sizeof(int)) &&
 	    (error = copyin(params, (caddr_t)args, (u_int)i))) {
-		mtx_lock(&Giant);
 #ifdef KTRACE
 		if (KTRPOINT(p, KTR_SYSCALL))
 			ktrsyscall(p->p_tracep, code, narg, args);
@@ -1110,8 +1106,6 @@ syscall(frame)
 	 * we are ktracing
 	 */
 	if (KTRPOINT(p, KTR_SYSCALL)) {
-		if (!mtx_owned(&Giant))
-			mtx_lock(&Giant);
 		ktrsyscall(p->p_tracep, code, narg, args);
 	}
 #endif
@@ -1157,8 +1151,6 @@ bad:
 	 * Traced syscall.
 	 */
 	if ((frame.tf_eflags & PSL_T) && !(frame.tf_eflags & PSL_VM)) {
-		if (!mtx_owned(&Giant))
-			mtx_lock(&Giant);
 		frame.tf_eflags &= ~PSL_T;
 		trapsignal(p, SIGTRAP, 0);
 	}
@@ -1170,17 +1162,18 @@ bad:
 
 #ifdef KTRACE
 	if (KTRPOINT(p, KTR_SYSRET)) {
-		if (!mtx_owned(&Giant))
-			mtx_lock(&Giant);
 		ktrsysret(p->p_tracep, code, error, p->p_retval[0]);
 	}
 #endif
 
 	/*
-	 * Release Giant if we had to get it
+	 * Release Giant if we previously set it.  Do not
+	 * release based on mtx_owned() - we want to catch
+	 * broken syscalls.
 	 */
-	if (mtx_owned(&Giant))
+	if ((callp->sy_narg & SYF_MPSAFE) == 0) {
 		mtx_unlock(&Giant);
+	}
 
 	/*
 	 * This works because errno is findable through the
@@ -1198,3 +1191,4 @@ bad:
 	mtx_assert(&sched_lock, MA_NOTOWNED);
 	mtx_assert(&Giant, MA_NOTOWNED);
 }
+
-- 
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