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, 3 insertions, 0 deletions

diff --git a/sys/kern/init_main.c b/sys/kern/init_main.c
index 4acc213..e984aec 100644
--- a/sys/kern/init_main.c
+++ b/sys/kern/init_main.c
@@ -358,6 +358,7 @@ proc0_init(void *dummy __unused)
 	/* Create the file descriptor table. */
 	fdp = &filedesc0;
 	p->p_fd = &fdp->fd_fd;
+	mtx_init(&fdp->fd_fd.fd_mtx, "struct filedesc", MTX_DEF);
 	fdp->fd_fd.fd_refcnt = 1;
 	fdp->fd_fd.fd_cmask = cmask;
 	fdp->fd_fd.fd_ofiles = fdp->fd_dfiles;
@@ -487,10 +488,12 @@ start_init(void *dummy)
 	/* Get the vnode for '/'.  Set p->p_fd->fd_cdir to reference it. */
 	if (VFS_ROOT(TAILQ_FIRST(&mountlist), &rootvnode))
 		panic("cannot find root vnode");
+	FILEDESC_LOCK(p->p_fd);
 	p->p_fd->fd_cdir = rootvnode;
 	VREF(p->p_fd->fd_cdir);
 	p->p_fd->fd_rdir = rootvnode;
 	VREF(p->p_fd->fd_rdir);
+	FILEDESC_UNLOCK(p->p_fd);
 	VOP_UNLOCK(rootvnode, 0, td);
 
 	if (devfs_present) {