[PATCH 15/15] RDMA/odp: Remove broken debugging call to invalidate_range

Jason Gunthorpe
2019-10-09T16:36:15Z

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(-)

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;
}

--
2.23.0