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/ufs/ffs/ffs_alloc.c b/sys/ufs/ffs/ffs_alloc.c
index e2fb3ab..321bf5a 100644
--- a/sys/ufs/ffs/ffs_alloc.c
+++ b/sys/ufs/ffs/ffs_alloc.c
@@ -1906,10 +1906,12 @@ sysctl_ffs_fsck(SYSCTL_HANDLER_ARGS)
 	vn_start_write((struct vnode *)fp->f_data, &mp, V_WAIT);
 	if (mp == 0 || strncmp(mp->mnt_stat.f_fstypename, "ufs", MFSNAMELEN)) {
 		vn_finished_write(mp);
+		fdrop(fp, curthread);
 		return (EINVAL);
 	}
 	if (mp->mnt_flag & MNT_RDONLY) {
 		vn_finished_write(mp);
+		fdrop(fp, curthread);
 		return (EROFS);
 	}
 	ump = VFSTOUFS(mp);
@@ -2041,6 +2043,7 @@ sysctl_ffs_fsck(SYSCTL_HANDLER_ARGS)
 		break;
 
 	}
+	fdrop(fp, curthread);
 	vn_finished_write(mp);
 	return (error);
 }