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btrfs: fix mount and ioctl device scan ioctl race
Technically this extends the critical section covered by uuid_mutex to: - parse early mount options -- here we can call device scan on paths that can be passed as 'device=/dev/...' - scan the device passed to mount - open the devices related to the fs_devices -- this increases fs_devices::opened The race can happen when mount calls one of the scans and there's another one called eg. by mkfs or 'btrfs dev scan': Mount Scan ----- ---- scan_one_device (dev1, fsid1) scan_one_device (dev2, fsid2) add the device free stale devices fsid1 fs_devices::opened == 0 find fsid1:dev1 free fsid1:dev1 if it's the last one, free fs_devices of fsid1 too open_devices (dev1, fsid1) dev1 not found When fixed, the uuid mutex will make sure that mount will increase fs_devices::opened and this will not be touched by the racing scan ioctl. Reported-and-tested-by: [email protected] Reported-and-tested-by: [email protected] Signed-off-by: David Sterba <[email protected]> Reviewed-by: Anand Jain <[email protected]>
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