[RFC PATCH v4 08/13] vfio: remove unnecessary mmap_sem writer acquisition around locked_vm

[Daniel Jordan]

Now that mmap_sem is no longer required for modifying locked_vm, remove
it in the VFIO code.

[XXX Can be sent separately, along with similar conversions in the other
places mmap_sem was taken for locked_vm.  While at it, could make
similar changes to pinned_vm.]

Signed-off-by: Daniel Jordan <daniel.m.jor...@oracle.com>
---
 drivers/vfio/vfio_iommu_type1.c | 26 +++++++++-----------------
 1 file changed, 9 insertions(+), 17 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index f307dc9d5e19..9e52a24eb45b 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -258,7 +258,8 @@ static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, 
struct vfio_pfn *vpfn)
 static int vfio_lock_acct(struct vfio_dma *dma, long npage, bool async)
 {
        struct mm_struct *mm;
-       int ret;
+       long locked_vm;
+       int ret = 0;
 
        if (!npage)
                return 0;
@@ -267,24 +268,15 @@ static int vfio_lock_acct(struct vfio_dma *dma, long 
npage, bool async)
        if (!mm)
                return -ESRCH; /* process exited */
 
-       ret = down_write_killable(&mm->mmap_sem);
-       if (!ret) {
-               if (npage > 0) {
-                       if (!dma->lock_cap) {
-                               unsigned long limit;
-
-                               limit = task_rlimit(dma->task,
-                                               RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+       locked_vm = atomic_long_add_return(npage, &mm->locked_vm);
 
-                               if (atomic_long_read(&mm->locked_vm) + npage > 
limit)
-                                       ret = -ENOMEM;
-                       }
+       if (npage > 0 && !dma->lock_cap) {
+               unsigned long limit = task_rlimit(dma->task, RLIMIT_MEMLOCK) >>
+                                         PAGE_SHIFT;
+               if (locked_vm > limit) {
+                       atomic_long_sub(npage, &mm->locked_vm);
+                       ret = -ENOMEM;
                }
-
-               if (!ret)
-                       atomic_long_add(npage, &mm->locked_vm);
-
-               up_write(&mm->mmap_sem);
        }
 
        if (async)
-- 
2.19.1