Hi Mike

Your idea looks good.

Thanks,
Sun Ke

在 2020/2/10 11:16, Mike Christie 写道:

On 01/19/2020 01:10 AM, sunke (E) wrote:

quoted

Thanks for your detailed suggestions.

在 2020/1/18 1:32, Mike Christie 写道:

quoted

On 01/17/2020 05:50 AM, Sun Ke wrote:

quoted

Connect and disconnect a nbd device repeatedly, will cause
NULL pointer fault.

It will appear by the steps:
1. Connect the nbd device and disconnect it, but now nbd device
     is not disconnected totally.
2. Connect the same nbd device again immediately, it will fail
     in nbd_start_device with a EBUSY return value.
3. Wait a second to make sure the last config_refs is reduced
     and run nbd_config_put to disconnect the nbd device totally.
4. Start another process to open the nbd_device, config_refs
     will increase and at the same time disconnect it.

Just to make sure I understood this, for step 4 the process is doing:

open(/dev/nbdX);
ioctl(NBD_DISCONNECT, /dev/nbdX) or nbd_genl_disconnect(for /dev/nbdX)

?

do nbd_genl_disconnect(for /dev/nbdX)；
I tested it. Connect /dev/nbdX
through ioctl interface by nbd-client -L -N export localhost /dev/nbdX and
through netlink interface by nbd-client localhost XXXX /dev/nbdX,
disconnect /dev/nbdX by nbd-client -d /dev/nbdX.
Both call nbd_genl_disconnect(for /dev/nbdX) and both contain the same
null pointer dereference.

quoted

There is no successful NBD_DO_IT / nbd_genl_connect between the open and
disconnect calls at step #4, because it would normally be done at #2 and
that failed. nbd_disconnect_and_put could then reference a null
recv_workq. If we are also racing with a close() then that could free
the device/config from under nbd_disconnect_and_put.

Yes, nbd_disconnect_and_put could then reference a null recv_workq.

Hey Sunke

How about the attached patch. I am still testing it. The basic idea is
that we need to do a flush whenever we have done a sock_shutdown and are
in the disconnect/connect/clear sock path, so it just adds the flush in
that function. We then do not need to keep adding these flushes everywhere.