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-rw-r--r--fs/block_dev.c198
1 files changed, 174 insertions, 24 deletions
diff --git a/fs/block_dev.c b/fs/block_dev.c
index e59440c7e1c..ea8385ea58a 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -694,11 +694,144 @@ static bool bd_may_claim(struct block_device *bdev, struct block_device *whole,
}
/**
+ * bd_prepare_to_claim - prepare to claim a block device
+ * @bdev: block device of interest
+ * @whole: the whole device containing @bdev, may equal @bdev
+ * @holder: holder trying to claim @bdev
+ *
+ * Prepare to claim @bdev. This function fails if @bdev is already
+ * claimed by another holder and waits if another claiming is in
+ * progress. This function doesn't actually claim. On successful
+ * return, the caller has ownership of bd_claiming and bd_holder[s].
+ *
+ * CONTEXT:
+ * spin_lock(&bdev_lock). Might release bdev_lock, sleep and regrab
+ * it multiple times.
+ *
+ * RETURNS:
+ * 0 if @bdev can be claimed, -EBUSY otherwise.
+ */
+static int bd_prepare_to_claim(struct block_device *bdev,
+ struct block_device *whole, void *holder)
+{
+retry:
+ /* if someone else claimed, fail */
+ if (!bd_may_claim(bdev, whole, holder))
+ return -EBUSY;
+
+ /* if someone else is claiming, wait for it to finish */
+ if (whole->bd_claiming && whole->bd_claiming != holder) {
+ wait_queue_head_t *wq = bit_waitqueue(&whole->bd_claiming, 0);
+ DEFINE_WAIT(wait);
+
+ prepare_to_wait(wq, &wait, TASK_UNINTERRUPTIBLE);
+ spin_unlock(&bdev_lock);
+ schedule();
+ finish_wait(wq, &wait);
+ spin_lock(&bdev_lock);
+ goto retry;
+ }
+
+ /* yay, all mine */
+ return 0;
+}
+
+/**
+ * bd_start_claiming - start claiming a block device
+ * @bdev: block device of interest
+ * @holder: holder trying to claim @bdev
+ *
+ * @bdev is about to be opened exclusively. Check @bdev can be opened
+ * exclusively and mark that an exclusive open is in progress. Each
+ * successful call to this function must be matched with a call to
+ * either bd_claim() or bd_abort_claiming(). If this function
+ * succeeds, the matching bd_claim() is guaranteed to succeed.
+ *
+ * CONTEXT:
+ * Might sleep.
+ *
+ * RETURNS:
+ * Pointer to the block device containing @bdev on success, ERR_PTR()
+ * value on failure.
+ */
+static struct block_device *bd_start_claiming(struct block_device *bdev,
+ void *holder)
+{
+ struct gendisk *disk;
+ struct block_device *whole;
+ int partno, err;
+
+ might_sleep();
+
+ /*
+ * @bdev might not have been initialized properly yet, look up
+ * and grab the outer block device the hard way.
+ */
+ disk = get_gendisk(bdev->bd_dev, &partno);
+ if (!disk)
+ return ERR_PTR(-ENXIO);
+
+ whole = bdget_disk(disk, 0);
+ put_disk(disk);
+ if (!whole)
+ return ERR_PTR(-ENOMEM);
+
+ /* prepare to claim, if successful, mark claiming in progress */
+ spin_lock(&bdev_lock);
+
+ err = bd_prepare_to_claim(bdev, whole, holder);
+ if (err == 0) {
+ whole->bd_claiming = holder;
+ spin_unlock(&bdev_lock);
+ return whole;
+ } else {
+ spin_unlock(&bdev_lock);
+ bdput(whole);
+ return ERR_PTR(err);
+ }
+}
+
+/* releases bdev_lock */
+static void __bd_abort_claiming(struct block_device *whole, void *holder)
+{
+ BUG_ON(whole->bd_claiming != holder);
+ whole->bd_claiming = NULL;
+ wake_up_bit(&whole->bd_claiming, 0);
+
+ spin_unlock(&bdev_lock);
+ bdput(whole);
+}
+
+/**
+ * bd_abort_claiming - abort claiming a block device
+ * @whole: whole block device returned by bd_start_claiming()
+ * @holder: holder trying to claim @bdev
+ *
+ * Abort a claiming block started by bd_start_claiming(). Note that
+ * @whole is not the block device to be claimed but the whole device
+ * returned by bd_start_claiming().
+ *
+ * CONTEXT:
+ * Grabs and releases bdev_lock.
+ */
+static void bd_abort_claiming(struct block_device *whole, void *holder)
+{
+ spin_lock(&bdev_lock);
+ __bd_abort_claiming(whole, holder); /* releases bdev_lock */
+}
+
+/**
* bd_claim - claim a block device
* @bdev: block device to claim
* @holder: holder trying to claim @bdev
*
- * Try to claim @bdev.
+ * Try to claim @bdev which must have been opened successfully. This
+ * function may be called with or without preceding
+ * blk_start_claiming(). In the former case, this function is always
+ * successful and terminates the claiming block.
+ *
+ * CONTEXT:
+ * Might sleep.
*
* RETURNS:
* 0 if successful, -EBUSY if @bdev is already claimed.
@@ -706,11 +839,14 @@ static bool bd_may_claim(struct block_device *bdev, struct block_device *whole,
int bd_claim(struct block_device *bdev, void *holder)
{
struct block_device *whole = bdev->bd_contains;
- int res = -EBUSY;
+ int res;
+
+ might_sleep();
spin_lock(&bdev_lock);
- if (bd_may_claim(bdev, whole, holder)) {
+ res = bd_prepare_to_claim(bdev, whole, holder);
+ if (res == 0) {
/* note that for a whole device bd_holders
* will be incremented twice, and bd_holder will
* be set to bd_claim before being set to holder
@@ -719,10 +855,13 @@ int bd_claim(struct block_device *bdev, void *holder)
whole->bd_holder = bd_claim;
bdev->bd_holders++;
bdev->bd_holder = holder;
- res = 0;
}
- spin_unlock(&bdev_lock);
+ if (whole->bd_claiming)
+ __bd_abort_claiming(whole, holder); /* releases bdev_lock */
+ else
+ spin_unlock(&bdev_lock);
+
return res;
}
EXPORT_SYMBOL(bd_claim);
@@ -1338,6 +1477,7 @@ EXPORT_SYMBOL(blkdev_get);
static int blkdev_open(struct inode * inode, struct file * filp)
{
+ struct block_device *whole = NULL;
struct block_device *bdev;
int res;
@@ -1360,22 +1500,25 @@ static int blkdev_open(struct inode * inode, struct file * filp)
if (bdev == NULL)
return -ENOMEM;
+ if (filp->f_mode & FMODE_EXCL) {
+ whole = bd_start_claiming(bdev, filp);
+ if (IS_ERR(whole)) {
+ bdput(bdev);
+ return PTR_ERR(whole);
+ }
+ }
+
filp->f_mapping = bdev->bd_inode->i_mapping;
res = blkdev_get(bdev, filp->f_mode);
- if (res)
- return res;
- if (filp->f_mode & FMODE_EXCL) {
- res = bd_claim(bdev, filp);
- if (res)
- goto out_blkdev_put;
+ if (whole) {
+ if (res == 0)
+ BUG_ON(bd_claim(bdev, filp) != 0);
+ else
+ bd_abort_claiming(whole, filp);
}
- return 0;
-
- out_blkdev_put:
- blkdev_put(bdev, filp->f_mode);
return res;
}
@@ -1586,27 +1729,34 @@ EXPORT_SYMBOL(lookup_bdev);
*/
struct block_device *open_bdev_exclusive(const char *path, fmode_t mode, void *holder)
{
- struct block_device *bdev;
- int error = 0;
+ struct block_device *bdev, *whole;
+ int error;
bdev = lookup_bdev(path);
if (IS_ERR(bdev))
return bdev;
+ whole = bd_start_claiming(bdev, holder);
+ if (IS_ERR(whole)) {
+ bdput(bdev);
+ return whole;
+ }
+
error = blkdev_get(bdev, mode);
if (error)
- return ERR_PTR(error);
+ goto out_abort_claiming;
+
error = -EACCES;
if ((mode & FMODE_WRITE) && bdev_read_only(bdev))
- goto blkdev_put;
- error = bd_claim(bdev, holder);
- if (error)
- goto blkdev_put;
+ goto out_blkdev_put;
+ BUG_ON(bd_claim(bdev, holder) != 0);
return bdev;
-
-blkdev_put:
+
+out_blkdev_put:
blkdev_put(bdev, mode);
+out_abort_claiming:
+ bd_abort_claiming(whole, holder);
return ERR_PTR(error);
}