SMP Lock struct file, filedesc and the global file list.

Seigo Tanimura (tanimura) posted the initial delta.

I've polished it quite a bit reducing the need for locking and
adapting it for KSE.

Locks:

1 mutex in each filedesc
   protects all the fields.
   protects "struct file" initialization, while a struct file
     is being changed from &badfileops -> &pipeops or something
     the filedesc should be locked.

1 mutex in each struct file
   protects the refcount fields.
   doesn't protect anything else.
   the flags used for garbage collection have been moved to
     f_gcflag which was the FILLER short, this doesn't need
     locking because the garbage collection is a single threaded
     container.
  could likely be made to use a pool mutex.

1 sx lock for the global filelist.

struct file *	fhold(struct file *fp);
        /* increments reference count on a file */

struct file *	fhold_locked(struct file *fp);
        /* like fhold but expects file to locked */

struct file *	ffind_hold(struct thread *, int fd);
        /* finds the struct file in thread, adds one reference and
                returns it unlocked */

struct file *	ffind_lock(struct thread *, int fd);
        /* ffind_hold, but returns file locked */

I still have to smp-safe the fget cruft, I'll get to that asap.

1 files changed, 8 insertions, 11 deletions

diff --git a/sys/vm/vm_mmap.c b/sys/vm/vm_mmap.c
index 015ef9b..9bf68c1 100644
--- a/sys/vm/vm_mmap.c
+++ b/sys/vm/vm_mmap.c
@@ -199,7 +199,6 @@ mmap(td, uap)
 	struct thread *td;
 	struct mmap_args *uap;
 {
-	struct filedesc *fdp = td->td_proc->p_fd;
 	struct file *fp = NULL;
 	struct vnode *vp;
 	vm_offset_t addr;
@@ -218,6 +217,7 @@ mmap(td, uap)
 	flags = uap->flags;
 	pos = uap->pos;
 
+	fp = NULL;
 	/* make sure mapping fits into numeric range etc */
 	if ((ssize_t) uap->len < 0 ||
 	    ((flags & MAP_ANON) && uap->fd != -1))
@@ -290,23 +290,19 @@ mmap(td, uap)
 		/*
 		 * Mapping file, get fp for validation. Obtain vnode and make
 		 * sure it is of appropriate type.
+		 * don't let the descriptor disappear on us if we block
 		 */
-		if (((unsigned) uap->fd) >= fdp->fd_nfiles ||
-		    (fp = fdp->fd_ofiles[uap->fd]) == NULL) {
+		fp = ffind_hold(td, uap->fd);
+		if (fp == NULL) {
 			error = EBADF;
-			goto done2;
+			goto done;
 		}
 		if (fp->f_type != DTYPE_VNODE) {
 			error = EINVAL;
-			goto done2;
+			goto done;
 		}
 
 		/*
-		 * don't let the descriptor disappear on us if we block
-		 */
-		fhold(fp);
-
-		/*
 		 * POSIX shared-memory objects are defined to have
 		 * kernel persistence, and are not defined to support
 		 * read(2)/write(2) -- or even open(2).  Thus, we can
@@ -437,7 +433,6 @@ mmap(td, uap)
 done:
 	if (fp)
 		fdrop(fp, td);
-done2:
 	mtx_unlock(&Giant);
 	return (error);
 }
@@ -642,7 +637,9 @@ munmapfd(td, fd)
 	/*
 	 * XXX should unmap any regions mapped to this file
 	 */
+	FILEDESC_LOCK(p->p_fd);
 	td->td_proc->p_fd->fd_ofileflags[fd] &= ~UF_MAPPED;
+	FILEDESC_UNLOCK(p->p_fd);
 }
 #endif