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, 4 insertions, 1 deletions

diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c
index 670d5dd..3fe2ab3 100644
--- a/sys/kern/kern_exec.c
+++ b/sys/kern/kern_exec.c
@@ -281,13 +281,16 @@ interpret:
 	 * For security and other reasons, the file descriptor table cannot
 	 * be shared after an exec.
 	 */
+	FILEDESC_LOCK(p->p_fd);
 	if (p->p_fd->fd_refcnt > 1) {
 		struct filedesc *tmp;
 
 		tmp = fdcopy(td);
+		FILEDESC_UNLOCK(p->p_fd);
 		fdfree(td);
 		p->p_fd = tmp;
-	}
+	} else
+		FILEDESC_UNLOCK(p->p_fd);
 
 	/*
 	 * For security and other reasons, signal handlers cannot