mtd: allow to unload the mtdtrans module if its block devices aren't open

[Linux-MTD Mailing List]

Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=008c751ec78587dd9b48bb62d4b10d616554fea2
Commit:     008c751ec78587dd9b48bb62d4b10d616554fea2
Parent:     ebd71e3a4861849054751779ff5ccd3fb29a1e0a
Author:     Maxim Levitsky <maximlevitsky at gmail.com>
AuthorDate: Fri Oct 15 17:20:43 2010 +0200
Committer:  David Woodhouse <David.Woodhouse at intel.com>
CommitDate: Mon Oct 25 01:28:30 2010 +0100

    mtd: allow to unload the mtdtrans module if its block devices aren't open
    
    Now it once again possible to remove mtdtrans module.
    You still need to ensure that block devices of that module aren't mounted.
    This is due to the fact that as long as a block device is open, it still exists,
    therefore if we were to allow module removal, this block device might became used again.
    
    This time in addition to code review, I also made the code
    pass some torture tests like module reload in  a loop + read in a loop +
    card insert/removal all at same time.
    
    The blktrans_open/blktrans_release don't take the mtd table lock because:
    
    While device is added (that includes execution of add_mtd_blktrans_dev)
    the lock is already taken
    
    Now suppose the device will never be removed. In this case even if we have changes
    in mtd table, the entry that we need will stay exactly the same. (Note that we don't
    look at table at all, just following private pointer of block device).
    
    Now suppose that someone tries to remove the mtd device.
    This will be propagated to trans driver which _ought_ to call del_mtd_blktrans_dev
    which will take the per device lock, release the mtd device and set trans->mtd = NULL.
    >From this point on, following opens won't even be able to know anything about that mtd device
    (which at that point is likely not to exist)
    Also the same care is taken not to trip over NULL mtd pointer in blktrans_dev_release.
    
    Signed-off-by: Maxim Levitsky <maximlevitsky at gmail.com>
    Tested-by: Artem Bityutskiy <Artem.Bityutskiy at nokia.com>
    Signed-off-by: David Woodhouse <David.Woodhouse at intel.com>
---
 drivers/mtd/mtd_blkdevs.c |   52 ++++++++++++++++++++------------------------
 1 files changed, 24 insertions(+), 28 deletions(-)

diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
index 62e6870..352831b 100644
--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -176,7 +176,7 @@ static void mtd_blktrans_request(struct request_queue *rq)
 static int blktrans_open(struct block_device *bdev, fmode_t mode)
 {
 	struct mtd_blktrans_dev *dev = blktrans_dev_get(bdev->bd_disk);
-	int ret;
+	int ret = 0;
 
 	if (!dev)
 		return -ERESTARTSYS; /* FIXME: busy loop! -arnd*/
@@ -184,17 +184,17 @@ static int blktrans_open(struct block_device *bdev, fmode_t mode)
 	lock_kernel();
 	mutex_lock(&dev->lock);
 
-	if (!dev->mtd) {
-		ret = -ENXIO;
+	if (dev->open++)
 		goto unlock;
-	}
 
-	ret = !dev->open++ && dev->tr->open ? dev->tr->open(dev) : 0;
+	kref_get(&dev->ref);
+	__module_get(dev->tr->owner);
+
+	if (dev->mtd) {
+		ret = dev->tr->open ? dev->tr->open(dev) : 0;
+		__get_mtd_device(dev->mtd);
+	}
 
-	/* Take another reference on the device so it won't go away till
-		last release */
-	if (!ret)
-		kref_get(&dev->ref);
 unlock:
 	mutex_unlock(&dev->lock);
 	blktrans_dev_put(dev);
@@ -205,7 +205,7 @@ unlock:
 static int blktrans_release(struct gendisk *disk, fmode_t mode)
 {
 	struct mtd_blktrans_dev *dev = blktrans_dev_get(disk);
-	int ret = -ENXIO;
+	int ret = 0;
 
 	if (!dev)
 		return ret;
@@ -213,13 +213,16 @@ static int blktrans_release(struct gendisk *disk, fmode_t mode)
 	lock_kernel();
 	mutex_lock(&dev->lock);
 
-	/* Release one reference, we sure its not the last one here*/
-	kref_put(&dev->ref, blktrans_dev_release);
-
-	if (!dev->mtd)
+	if (--dev->open)
 		goto unlock;
 
-	ret = !--dev->open && dev->tr->release ? dev->tr->release(dev) : 0;
+	kref_put(&dev->ref, blktrans_dev_release);
+	module_put(dev->tr->owner);
+
+	if (dev->mtd) {
+		ret = dev->tr->release ? dev->tr->release(dev) : 0;
+		__put_mtd_device(dev->mtd);
+	}
 unlock:
 	mutex_unlock(&dev->lock);
 	blktrans_dev_put(dev);
@@ -385,9 +388,6 @@ int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
 
 	gd->queue = new->rq;
 
-	__get_mtd_device(new->mtd);
-	__module_get(tr->owner);
-
 	/* Create processing thread */
 	/* TODO: workqueue ? */
 	new->thread = kthread_run(mtd_blktrans_thread, new,
@@ -410,8 +410,6 @@ int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
 	}
 	return 0;
 error4:
-	module_put(tr->owner);
-	__put_mtd_device(new->mtd);
 	blk_cleanup_queue(new->rq);
 error3:
 	put_disk(new->disk);
@@ -448,17 +446,15 @@ int del_mtd_blktrans_dev(struct mtd_blktrans_dev *old)
 	blk_start_queue(old->rq);
 	spin_unlock_irqrestore(&old->queue_lock, flags);
 
-	/* Ask trans driver for release to the mtd device */
+	/* If the device is currently open, tell trans driver to close it,
+		then put mtd device, and don't touch it again */
 	mutex_lock(&old->lock);
-	if (old->open && old->tr->release) {
-		old->tr->release(old);
-		old->open = 0;
+	if (old->open) {
+		if (old->tr->release)
+			old->tr->release(old);
+		__put_mtd_device(old->mtd);
 	}
 
-	__put_mtd_device(old->mtd);
-	module_put(old->tr->owner);
-
-	/* At that point, we don't touch the mtd anymore */
 	old->mtd = NULL;
 
 	mutex_unlock(&old->lock);