On 14/12/19 1:02 AM, David Sterba wrote:
On Fri, Dec 13, 2019 at 05:43:32PM +0100, David Sterba wrote:
Looked into this further, actually we don't need any lock here
the device delete thread which calls kobject_put() makes sure
sysfs read is closed. So an existing sysfs read thread will have
to complete before device free.
CPU1 CPU2
btrfs_rm_device
open file
btrfs_sysfs_rm_device_link
call read, access freed device
sysfs waits for the open file
to close.
How exactly does sysfs wait for the device? Is it eg wait_event checking
number of references? If the file stays open by an evil process is it
going to block the device removal indefinitelly?
Yeah, sysfs waits until the file is closed. Eg. umount can be stalled
that way too.
And similar to umount, I don't think we should return EBUSY
for btrfs_rm_device if the device sysfs attribute is opened,
as sysfs show attributes are non blocking and would be completed
in the timely manner.
regards, Anand
