Revert "net/rds: Avoid potential use after free in rds_send_remove_from_sock"

This reverts commit 0c85a7e874.

The games with 'rm' are on (two separate instances) of a local variable,
and make no difference.

Quoting Aditya Pakki:
 "I was the author of the patch and it was the cause of the giant UMN
  revert.

  The patch is garbage and I was unaware of the steps involved in
  retracting it. I *believed* the maintainers would pull it, given it
  was already under Greg's list. The patch does not introduce any bugs
  but is pointless and is stupid. I accept my incompetence and for not
  requesting a revert earlier."

Link: https://lwn.net/Articles/854319/
Requested-by: Aditya Pakki <pakki001@umn.edu>
Cc: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

net/rds/message.c

@@ -180,7 +180,6 @@ void rds_message_put(struct rds_message *rm)
 		rds_message_purge(rm);
 
 		kfree(rm);
-		rm = NULL;
 	}
 }
 EXPORT_SYMBOL_GPL(rds_message_put);

net/rds/send.c

@@ -665,7 +665,7 @@ static void rds_send_remove_from_sock(struct list_head *messages, int status)
 unlock_and_drop:
 		spin_unlock_irqrestore(&rm->m_rs_lock, flags);
 		rds_message_put(rm);
-		if (was_on_sock && rm)
+		if (was_on_sock)
 			rds_message_put(rm);
 	}