IB/hfi1: Reserve user expected TIDs

To avoid a race, reserve the number of user expected
TIDs before setup.

Fixes: 7e7a436e ("staging/hfi1: Add TID entry program function body")
Signed-off-by: Dean Luick <dean.luick@cornelisnetworks.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Link: https://lore.kernel.org/r/167328547636.1472310.7419712824785353905.stgit@awfm-02.cornelisnetworks.comSigned-off-by: Leon Romanovsky <leon@kernel.org>

drivers/infiniband/hw/hfi1/user_exp_rcv.c

@@ -282,16 +282,13 @@ int hfi1_user_exp_rcv_setup(struct hfi1_filedata *fd,
 	/* Find sets of physically contiguous pages */
 	tidbuf->n_psets = find_phys_blocks(tidbuf, pinned);
 
-	/*
-	 * We don't need to access this under a lock since tid_used is per
-	 * process and the same process cannot be in hfi1_user_exp_rcv_clear()
-	 * and hfi1_user_exp_rcv_setup() at the same time.
-	 */
+	/* Reserve the number of expected tids to be used. */
 	spin_lock(&fd->tid_lock);
 	if (fd->tid_used + tidbuf->n_psets > fd->tid_limit)
 		pageset_count = fd->tid_limit - fd->tid_used;
 	else
 		pageset_count = tidbuf->n_psets;
+	fd->tid_used += pageset_count;
 	spin_unlock(&fd->tid_lock);
 
 	if (!pageset_count)
@@ -400,10 +397,11 @@ int hfi1_user_exp_rcv_setup(struct hfi1_filedata *fd,
 nomem:
 	hfi1_cdbg(TID, "total mapped: tidpairs:%u pages:%u (%d)", tididx,
 		  mapped_pages, ret);
+	/* adjust reserved tid_used to actual count */
+	spin_lock(&fd->tid_lock);
+	fd->tid_used -= pageset_count - tididx;
+	spin_unlock(&fd->tid_lock);
 	if (tididx) {
-		spin_lock(&fd->tid_lock);
-		fd->tid_used += tididx;
-		spin_unlock(&fd->tid_lock);
 		tinfo->tidcnt = tididx;
 		tinfo->length = mapped_pages * PAGE_SIZE;