Re: [PATCH v1 01/12] IB/core: pass client data to remove() callbacks

On 09/07/2015 00:34, Jason Gunthorpe wrote:

On Wed, Jul 08, 2015 at 02:29:10PM -0600, Jason Gunthorpe wrote:

quoted

On Mon, Jun 22, 2015 at 03:42:30PM +0300, Haggai Eran wrote:

quoted

An ib_client callback that is called with the lists_rwsem locked only for
read is protected from changes to the IB client lists, but not from
ib_unregister_device() freeing its client data. This is because
ib_unregister_device() will remove the device from the device list with
lists_rwsem locked for write, but perform the rest of the cleanup,
including the call to remove() without that lock.

I was going to look at this, but, uh.. it seems mangled, doesn't
apply, doesn't seem fixable from here.

Okay, I see, it sits on top of the patch from Matan's last
posting.. My bad.

No problem.

Hum... I have to say I don't really like this, changing the ordering
of client_data = NULL with respect to client->remove doesn't seem like
a great idea - and the rds changes look scary to me, at least I
couldn't confidently say they were OK..

And that isn't really the issue - this has nothing to do with
client_data, it is all about not having a callback running when doing
remove.

It looks like the way out of this is to have ib_get_net_dev_by_params
iterate over the client_data_list and use a dedicated flag in that
struct to indicate that client&device combination is
remove-in-progress.

This would be a bit more efficient as well, and I would suggest
passing the context in as an arg to the callback.

client_data_list would change a bit to become write locked first by
write(lists_rwsem), and then second by the spin lock, so holding
read(lists_rwsem) while iterating is enough locking, and you'd hold
lists_rwsem while kfreeing.

So, I don't want to keep lists_rwsem for write while calling add() and
remove(). This would cause the deadlock that required the lists_rwsem
patch in the first place. I guess I can drop lists_rwsem before the
add/remove call and take it afterwards.

Haggai
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