From: Martin Pieuchot <mpi@grenadille.net>
Subject: Push KERNEL_LOCK() into open(2) & openat(2)
To: tech@openbsd.org
Date: Wed, 22 Jan 2025 12:01:49 +0100

Here's the next step from my VFS unlock diff sent some weeks ago.

This one pushes the KERNEL_LOCK() around vn_open() in doopenat().  This
should give a small boost and make contention clearer in FlameGraphs.

ok?

Index: kern/syscalls.master
===================================================================
RCS file: /cvs/src/sys/kern/syscalls.master,v
diff -u -p -r1.265 syscalls.master
--- kern/syscalls.master	2 Aug 2024 14:34:45 -0000	1.265
+++ kern/syscalls.master	28 Nov 2024 18:55:36 -0000
@@ -52,7 +52,7 @@
 3	STD NOLOCK	{ ssize_t sys_read(int fd, void *buf, size_t nbyte); }
 4	STD NOLOCK	{ ssize_t sys_write(int fd, const void *buf, \
 			    size_t nbyte); }
-5	STD		{ int sys_open(const char *path, \
+5	STD NOLOCK	{ int sys_open(const char *path, \
 			    int flags, ... mode_t mode); }
 6	STD NOLOCK	{ int sys_close(int fd); }
 7	STD NOLOCK	{ int sys_getentropy(void *buf, size_t nbyte); }
@@ -553,7 +553,7 @@
 			    mode_t mode); }
 320	STD		{ int sys_mknodat(int fd, const char *path, \
 			    mode_t mode, dev_t dev); }
-321	STD		{ int sys_openat(int fd, const char *path, int flags, \
+321	STD NOLOCK	{ int sys_openat(int fd, const char *path, int flags, \
 			    ... mode_t mode); }
 322	STD		{ ssize_t sys_readlinkat(int fd, const char *path, \
 			    char *buf, size_t count); }
Index: kern/vfs_syscalls.c
===================================================================
RCS file: /cvs/src/sys/kern/vfs_syscalls.c,v
diff -u -p -r1.370 vfs_syscalls.c
--- kern/vfs_syscalls.c	5 Nov 2024 06:03:19 -0000	1.370
+++ kern/vfs_syscalls.c	28 Nov 2024 18:19:24 -0000
@@ -1120,23 +1126,20 @@ doopenat(struct proc *p, int fd, const c
 		localtrunc = 1;
 		flags &= ~O_TRUNC;	/* Must do truncate ourselves */
 	}
+	KERNEL_LOCK();
 	if ((error = vn_open(&nd, flags, cmode)) != 0) {
 		fdplock(fdp);
 		if (error == ENODEV &&
 		    p->p_dupfd >= 0 &&			/* XXX from fdopen */
 		    (error =
 			dupfdopen(p, indx, flags)) == 0) {
-			fdpunlock(fdp);
-			closef(fp, p);
 			*retval = indx;
-			return (error);
+			goto error;
 		}
 		if (error == ERESTART)
 			error = EINTR;
 		fdremove(fdp, indx);
-		fdpunlock(fdp);
-		closef(fp, p);
-		return (error);
+		goto error;
 	}
 	p->p_dupfd = 0;
 	vp = nd.ni_vp;
@@ -1161,9 +1164,7 @@ doopenat(struct proc *p, int fd, const c
 			fdplock(fdp);
 			/* closef will vn_close the file for us. */
 			fdremove(fdp, indx);
-			fdpunlock(fdp);
-			closef(fp, p);
-			return (error);
+			goto error;
 		}
 		vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 		atomic_setbits_int(&fp->f_iflags, FIF_HASLOCK);
@@ -1185,18 +1186,22 @@ doopenat(struct proc *p, int fd, const c
 			fdplock(fdp);
 			/* closef will close the file for us. */
 			fdremove(fdp, indx);
-			fdpunlock(fdp);
-			closef(fp, p);
-			return (error);
+			goto error;
 		}
 	}
 	VOP_UNLOCK(vp);
+	KERNEL_UNLOCK();
 	*retval = indx;
 	fdplock(fdp);
 	fdinsert(fdp, indx, cloexec, fp);
 	fdpunlock(fdp);
 	FRELE(fp, p);
 	return (error);
+error:
+	KERNEL_UNLOCK();
+	fdpunlock(fdp);
+	closef(fp, p);
+	return (error);
 }
 
 /*