[PATCH] RDMA/siw: Fix user page pinning accounting

[Bernard Metzler <bmt@zurich.ibm.com>]

To avoid racing with other user memory reservations, immediately
account full amount of pages to be pinned.

Fixes: 2251334dcac9 ("rdma/siw: application buffer management")
Reported-by: Jason Gunthorpe <jgg@nvidia.com>
Suggested-by: Alistair Popple <apopple@nvidia.com>
Signed-off-by: Bernard Metzler <bmt@zurich.ibm.com>
---
 drivers/infiniband/sw/siw/siw_mem.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/sw/siw/siw_mem.c b/drivers/infiniband/sw/siw/siw_mem.c
index b2b33dd3b4fa..7afdbe3f2266 100644
--- a/drivers/infiniband/sw/siw/siw_mem.c
+++ b/drivers/infiniband/sw/siw/siw_mem.c
@@ -398,7 +398,7 @@ struct siw_umem *siw_umem_get(u64 start, u64 len, bool writable)
 
 	mlock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
 
-	if (num_pages + atomic64_read(&mm_s->pinned_vm) > mlock_limit) {
+	if (atomic64_add_return(num_pages, &mm_s->pinned_vm) > mlock_limit) {
 		rv = -ENOMEM;
 		goto out_sem_up;
 	}
@@ -429,7 +429,6 @@ struct siw_umem *siw_umem_get(u64 start, u64 len, bool writable)
 				goto out_sem_up;
 
 			umem->num_pages += rv;
-			atomic64_add(rv, &mm_s->pinned_vm);
 			first_page_va += rv * PAGE_SIZE;
 			nents -= rv;
 			got += rv;
@@ -442,6 +441,10 @@ struct siw_umem *siw_umem_get(u64 start, u64 len, bool writable)
 	if (rv > 0)
 		return umem;
 
+	/* Adjust accounting for pages not pinned */
+	if (num_pages)
+		atomic64_sub(num_pages, &mm_s->pinned_vm);
+
 	siw_umem_release(umem, false);
 
 	return ERR_PTR(rv);
-- 
2.32.0