At present, it is not possible to successfully unload the kafs module if there
are outstanding async outgoing calls (those made with afs_make_call()). This
appears to be due to the changes introduced by:
commit 059499453a
Author: Tejun Heo <tj@kernel.org>
Date: Fri Mar 7 10:24:50 2014 -0500
Subject: afs: don't use PREPARE_WORK
which didn't go far enough. The problem is due to:
(1) The aforementioned commit introduced a separate handler function pointer
in the call, call->async_workfn, in addition to the original workqueue
item, call->async_work, for asynchronous operations because workqueues
subsystem cannot handle the workqueue item pointer being changed whilst
the item is queued or being processed.
(2) afs_async_workfn() was introduced in that commit to be the callback for
call->async_work. Its sole purpose is to run whatever call->async_workfn
points to.
(3) call->async_workfn is only used from afs_async_workfn(), which is only
set on async_work by afs_collect_incoming_call() - ie. for incoming
calls.
(4) call->async_workfn is *not* set by afs_make_call() when outgoing calls are
made, and call->async_work is set afs_process_async_call() - and not
afs_async_workfn().
(5) afs_process_async_call() now changes call->async_workfn rather than
call->async_work to point to afs_delete_async_call() to clean up, but this
is only effective for incoming calls because call->async_work does not
point to afs_async_workfn() for outgoing calls.
(6) Because, for incoming calls, call->async_work remains pointing to
afs_process_async_call() this results in an infinite loop.
Instead, make the workqueue uniformly vector through call->async_workfn, via
afs_async_workfn() and simply initialise call->async_workfn to point to
afs_process_async_call() in afs_make_call().
Signed-off-by: Nathaniel Wesley Filardo <nwf@cs.jhu.edu>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Tejun Heo <tj@kernel.org>
150a6b4789