Revert "[PATCH] kthread: update loop.c to use kthread"

This reverts commit c7b2eff059fcc2d1b7085ee3d84b79fd657a537b.

Hugh Dickins explains:

 "It seems too little tested: "losetup -d /dev/loop0" fails with
  EINVAL because nothing sets lo_thread; but even when you patch
  loop_thread() to set lo->lo_thread = current, it can't survive
  more than a few dozen iterations of the loop below (with a tmpfs
  mounted on /tst):

	j=0
	cp /dev/zero /tst
	while :
	do
	    let j=j+1
	    echo "Doing pass $j"
	    losetup /dev/loop0 /tst/zero
	    mkfs -t ext2 -b 1024 /dev/loop0 >/dev/null 2>&1
	    mount -t ext2 /dev/loop0 /mnt
	    umount /mnt
	    losetup -d /dev/loop0
	done

  it collapses with failed ioctl then BUG_ON(!bio).

  I think the original lo_done completion was more subtle and safe
  than the kthread conversion has allowed for."

Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 14 insertions, 12 deletions

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 9dc294a7495..3c74ea729fc 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -74,7 +74,6 @@
 #include <linux/completion.h>
 #include <linux/highmem.h>
 #include <linux/gfp.h>
-#include <linux/kthread.h>
 
 #include <asm/uaccess.h>
 
@@ -579,6 +578,8 @@ static int loop_thread(void *data)
         struct loop_device *lo = data;
         struct bio *bio;
 
+        daemonize("loop%d", lo->lo_number);
+
         /*
          * loop can be used in an encrypted device,
          * hence, it mustn't be stopped at all
@@ -591,6 +592,11 @@ static int loop_thread(void *data)
         lo->lo_state = Lo_bound;
         lo->lo_pending = 1;
 
+        /*
+         * complete it, we are running
+         */
+        complete(&lo->lo_done);
+
         for (;;) {
                 int pending;
 
@@ -623,6 +629,7 @@ static int loop_thread(void *data)
                         break;
         }
 
+        complete(&lo->lo_done);
         return 0;
 }
 
@@ -739,7 +746,6 @@ static int loop_set_fd(struct loop_device *lo, struct file *lo_file,
         unsigned lo_blocksize;
         int             lo_flags = 0;
         int             error;
-        struct task_struct *tsk;
         loff_t          size;
 
         /* This is safe, since we have a reference from open(). */
@@ -833,11 +839,10 @@ static int loop_set_fd(struct loop_device *lo, struct file *lo_file,
 
         set_blocksize(bdev, lo_blocksize);
 
-        tsk = kthread_run(loop_thread, lo, "loop%d", lo->lo_number);
-        if (IS_ERR(tsk)) {
-                error = PTR_ERR(tsk);
+        error = kernel_thread(loop_thread, lo, CLONE_KERNEL);
+        if (error < 0)
                 goto out_putf;
-        }
+        wait_for_completion(&lo->lo_done);
         return 0;
 
  out_putf:
@@ -893,9 +898,6 @@ static int loop_clr_fd(struct loop_device *lo, struct block_device *bdev)
         if (lo->lo_state != Lo_bound)
                 return -ENXIO;
 
-        if (!lo->lo_thread)
-                return -EINVAL;
-
         if (lo->lo_refcnt > 1)  /* we needed one fd for the ioctl */
                 return -EBUSY;
 
@@ -909,7 +911,7 @@ static int loop_clr_fd(struct loop_device *lo, struct block_device *bdev)
                 complete(&lo->lo_bh_done);
         spin_unlock_irq(&lo->lo_lock);
 
-        kthread_stop(lo->lo_thread);
+        wait_for_completion(&lo->lo_done);
 
         lo->lo_backing_file = NULL;
 
@@ -922,7 +924,6 @@ static int loop_clr_fd(struct loop_device *lo, struct block_device *bdev)
         lo->lo_sizelimit = 0;
         lo->lo_encrypt_key_size = 0;
         lo->lo_flags = 0;
-        lo->lo_thread = NULL;
         memset(lo->lo_encrypt_key, 0, LO_KEY_SIZE);
         memset(lo->lo_crypt_name, 0, LO_NAME_SIZE);
         memset(lo->lo_file_name, 0, LO_NAME_SIZE);
@@ -1287,6 +1288,7 @@ static int __init loop_init(void)
                 if (!lo->lo_queue)
                         goto out_mem4;
                 mutex_init(&lo->lo_ctl_mutex);
+                init_completion(&lo->lo_done);
                 init_completion(&lo->lo_bh_done);
                 lo->lo_number = i;
                 spin_lock_init(&lo->lo_lock);
diff --git a/include/linux/loop.h b/include/linux/loop.h
index bf3d2345ce9..e76c7611d6c 100644
--- a/include/linux/loop.h
+++ b/include/linux/loop.h
@@ -59,7 +59,7 @@ struct loop_device {
         struct bio              *lo_bio;
         struct bio              *lo_biotail;
         int                     lo_state;
-        struct task_struct      *lo_thread;
+        struct completion       lo_done;
         struct completion       lo_bh_done;
         struct mutex            lo_ctl_mutex;
         int                     lo_pending;