[15/15] RDMA/odp: Remove broken debugging call to invalidate_range
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Message ID 20191009160934.3143-16-jgg@ziepe.ca
State Accepted
Delegated to: Jason Gunthorpe
Headers show
Series
  • Rework the locking and datastructures for mlx5 implicit ODP
Related show

Commit Message

Jason Gunthorpe Oct. 9, 2019, 4:09 p.m. UTC
From: Jason Gunthorpe <jgg@mellanox.com>

invalidate_range() also obtains the umem_mutex which is being held at this
point, so if this path were was ever called it would deadlock. Thus
conclude the debugging never triggers and rework it into a simple WARN_ON
and leave things as they are.

While here add a note to explain how we could possibly get inconsistent
page pointers.

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
---
 drivers/infiniband/core/umem_odp.c | 38 +++++++++++++++---------------
 1 file changed, 19 insertions(+), 19 deletions(-)

Patch
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diff --git a/drivers/infiniband/core/umem_odp.c b/drivers/infiniband/core/umem_odp.c
index 163ff7ba92b7f1..d7d5fadf0899ad 100644
--- a/drivers/infiniband/core/umem_odp.c
+++ b/drivers/infiniband/core/umem_odp.c
@@ -508,7 +508,6 @@  static int ib_umem_odp_map_dma_single_page(
 {
 	struct ib_device *dev = umem_odp->umem.ibdev;
 	dma_addr_t dma_addr;
-	int remove_existing_mapping = 0;
 	int ret = 0;
 
 	/*
@@ -534,28 +533,29 @@  static int ib_umem_odp_map_dma_single_page(
 	} else if (umem_odp->page_list[page_index] == page) {
 		umem_odp->dma_list[page_index] |= access_mask;
 	} else {
-		pr_err("error: got different pages in IB device and from get_user_pages. IB device page: %p, gup page: %p\n",
-		       umem_odp->page_list[page_index], page);
-		/* Better remove the mapping now, to prevent any further
-		 * damage. */
-		remove_existing_mapping = 1;
+		/*
+		 * This is a race here where we could have done:
+		 *
+		 *         CPU0                             CPU1
+		 *   get_user_pages()
+		 *                                       invalidate()
+		 *                                       page_fault()
+		 *   mutex_lock(umem_mutex)
+		 *    page from GUP != page in ODP
+		 *
+		 * It should be prevented by the retry test above as reading
+		 * the seq number should be reliable under the
+		 * umem_mutex. Thus something is really not working right if
+		 * things get here.
+		 */
+		WARN(true,
+		     "Got different pages in IB device and from get_user_pages. IB device page: %p, gup page: %p\n",
+		     umem_odp->page_list[page_index], page);
+		ret = -EAGAIN;
 	}
 
 out:
 	put_user_page(page);
-
-	if (remove_existing_mapping) {
-		ib_umem_notifier_start_account(umem_odp);
-		dev->ops.invalidate_range(
-			umem_odp,
-			ib_umem_start(umem_odp) +
-				(page_index << umem_odp->page_shift),
-			ib_umem_start(umem_odp) +
-				((page_index + 1) << umem_odp->page_shift));
-		ib_umem_notifier_end_account(umem_odp);
-		ret = -EAGAIN;
-	}
-
 	return ret;
 }