IB/uverbs: Rework the locking for cleaning up the ucontext

The locking here has always been a bit crazy and spread out, upon some
careful analysis we can simplify things.

Create a single function uverbs_destroy_ufile_hw() that internally handles
all locking. This pulls together pieces of this process that were
sprinkled all over the places into one place, and covers them with one
lock.

This eliminates several duplicate/confusing locks and makes the control
flow in ib_uverbs_close() and ib_uverbs_free_hw_resources() extremely
simple.

Unfortunately we have to keep an extra mutex, ucontext_lock.  This lock is
logically part of the rwsem and provides the 'down write, fail if write
locked, wait if read locked' semantic we require.

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index 99bcf64a4762..42cbf8eabe9d 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -1479,6 +1479,11 @@ struct ib_rdmacg_object {
 struct ib_ucontext {
 	struct ib_device       *device;
 	struct ib_uverbs_file  *ufile;
+	/*
+	 * 'closing' can be read by the driver only during a destroy callback,
+	 * it is set when we are closing the file descriptor and indicates
+	 * that mm_sem may be locked.
+	 */
 	int			closing;
 
 	bool cleanup_retryable;