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Subject[PATCH] lightnvm: prevent bd removal if busy
Removal of virtual block device by "nvm lnvm remove..." undergoing IO
and created by "nvme lnvm create... -t pblk" results in following and
is annoying.

446416.309757] bdi-block not registered
[446416.309773] ------------[ cut here ]------------
[446416.309780] WARNING: CPU: 3 PID: 4319 at fs/fs-writeback.c:2159 __mark_inode_dirty+0x268/0x340
.....

This patch solves this by checking bd_openers for each partition
before removal can continue. Note that this isn't full proof as
device can become busy as soon as it's bd_mutex is unlocked but it
needn't be full proof either. It does work for general case where
device is mounted and removal can be prevented.

Signed-off-by: Rakesh Pandit <rakesh@tuxera.com>
---
drivers/lightnvm/core.c | 42 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 42 insertions(+)

diff --git a/drivers/lightnvm/core.c b/drivers/lightnvm/core.c
index bbea2c8..cff91c7 100644
--- a/drivers/lightnvm/core.c
+++ b/drivers/lightnvm/core.c
@@ -369,6 +369,10 @@ static void __nvm_remove_target(struct nvm_target *t)
static int nvm_remove_tgt(struct nvm_dev *dev, struct nvm_ioctl_remove *remove)
{
struct nvm_target *t;
+ struct gendisk *tdisk;
+ struct disk_part_iter piter;
+ struct hd_struct *part;
+ int err;

mutex_lock(&dev->mlock);
t = nvm_find_target(dev, remove->tgtname);
@@ -376,10 +380,48 @@ static int nvm_remove_tgt(struct nvm_dev *dev, struct nvm_ioctl_remove *remove)
mutex_unlock(&dev->mlock);
return 1;
}
+
+ /*
+ * Lets make sure device is not in use. Note that this isn't full proof
+ * in anyway (as devices can become busy after unlock) but it is useful
+ * for preventing removal of devices which are open and undergoing IO.
+ */
+ tdisk = t->disk;
+ disk_part_iter_init(&piter, tdisk,
+ DISK_PITER_INCL_EMPTY | DISK_PITER_INCL_PART0 |
+ DISK_PITER_INCL_EMPTY_PART0);
+ while ((part = disk_part_iter_next(&piter))) {
+ struct block_device *bdev;
+
+ bdev = bdget(part_devt(part));
+ if (!bdev) {
+ err = -ENOMEM;
+ pr_err("nvm: removal failed, allocating bd failed\n");
+ goto err_out;
+ }
+ mutex_lock(&bdev->bd_mutex);
+ if (bdev->bd_openers) {
+ mutex_unlock(&bdev->bd_mutex);
+ bdput(bdev);
+ err = -EBUSY;
+ pr_err("nvm: removal failed, block device busy\n");
+ goto err_out;
+ }
+ mutex_unlock(&bdev->bd_mutex);
+ bdput(bdev);
+ }
+ disk_part_iter_exit(&piter);
+
__nvm_remove_target(t);
mutex_unlock(&dev->mlock);

return 0;
+err_out:
+ disk_part_iter_exit(&piter);
+ disk_put_part(part);
+ mutex_unlock(&dev->mlock);
+
+ return err;
}

static int nvm_register_map(struct nvm_dev *dev)
--
2.7.4
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