drbd: fix harmless race to not trigger an ASSERT
We have one pre-allocated page to do certain synchronous meta data IO with,
using it is serialized like so:
drbd_md_get_buffer();
drbd_md_sync_page_io();
drbd_md_sync_page_io();
...
drbd_md_put_buffer();
In drbd_md_sync_page_io() there is an
ASSERT(atomic_read(&mdev->md_io_in_use) == 1);
We want to be able to timeout on unresponsive lower level devices, so we
can "detach" in that case. Inside drbd_md_sync_page_io() we grab an extra
reference, to not have a dangling pointer in case a delayed IO eventually
does still complete, even after we "detached" already.
We need to put the extra reference before we signal completion from the
completion handler, or the second drbd_md_sync_page_io() above may
trigger the assert (reference count still 2).
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
1 file changed