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Subject[PATCH 4.9 12/16] rbd: dont return 0 on unmap if RBD_DEV_FLAG_REMOVING is set
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ilya Dryomov <idryomov@gmail.com>

commit 85f5a4d666fd9be73856ed16bb36c5af5b406b29 upstream.

There is a window between when RBD_DEV_FLAG_REMOVING is set and when
the device is removed from rbd_dev_list. During this window, we set
"already" and return 0.

Returning 0 from write(2) can confuse userspace tools because
0 indicates that nothing was written. In particular, "rbd unmap"
will retry the write multiple times a second:

10:28:05.463299 write(4, "0", 1) = 0
10:28:05.463509 write(4, "0", 1) = 0
10:28:05.463720 write(4, "0", 1) = 0
10:28:05.463942 write(4, "0", 1) = 0
10:28:05.464155 write(4, "0", 1) = 0

Cc: stable@vger.kernel.org
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Tested-by: Dongsheng Yang <dongsheng.yang@easystack.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/block/rbd.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)

--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -6346,7 +6346,6 @@ static ssize_t do_rbd_remove(struct bus_
struct list_head *tmp;
int dev_id;
char opt_buf[6];
- bool already = false;
bool force = false;
int ret;

@@ -6379,13 +6378,13 @@ static ssize_t do_rbd_remove(struct bus_
spin_lock_irq(&rbd_dev->lock);
if (rbd_dev->open_count && !force)
ret = -EBUSY;
- else
- already = test_and_set_bit(RBD_DEV_FLAG_REMOVING,
- &rbd_dev->flags);
+ else if (test_and_set_bit(RBD_DEV_FLAG_REMOVING,
+ &rbd_dev->flags))
+ ret = -EINPROGRESS;
spin_unlock_irq(&rbd_dev->lock);
}
spin_unlock(&rbd_dev_list_lock);
- if (ret < 0 || already)
+ if (ret)
return ret;

if (force) {

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