[PATCH 3/6] vfio/spapr_tce: drop mmap_sem now that locked_vm is atomic

[Daniel Jordan]

With locked_vm now an atomic, there is no need to take mmap_sem as
writer.  Delete and refactor accordingly.

Signed-off-by: Daniel Jordan <daniel.m.jor...@oracle.com>
Cc: Alexey Kardashevskiy <a...@ozlabs.ru>
Cc: Alex Williamson <alex.william...@redhat.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Christoph Lameter <c...@linux.com>
Cc: Davidlohr Bueso <d...@stgolabs.net>
Cc: <linux...@kvack.org>
Cc: <k...@vger.kernel.org>
Cc: <linux-kernel@vger.kernel.org>
---
 drivers/vfio/vfio_iommu_spapr_tce.c | 36 ++++++++++++-----------------
 1 file changed, 15 insertions(+), 21 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c 
b/drivers/vfio/vfio_iommu_spapr_tce.c
index e7d787e5d839..7675a3b28410 100644
--- a/drivers/vfio/vfio_iommu_spapr_tce.c
+++ b/drivers/vfio/vfio_iommu_spapr_tce.c
@@ -36,8 +36,9 @@ static void tce_iommu_detach_group(void *iommu_data,
 
 static long try_increment_locked_vm(struct mm_struct *mm, long npages)
 {
-       long ret = 0, lock_limit;
+       long ret = 0;
        s64 locked;
+       unsigned long lock_limit;
 
        if (WARN_ON_ONCE(!mm))
                return -EPERM;
@@ -45,39 +46,32 @@ static long try_increment_locked_vm(struct mm_struct *mm, 
long npages)
        if (!npages)
                return 0;
 
-       down_write(&mm->mmap_sem);
-       locked = atomic64_read(&mm->locked_vm) + npages;
+       locked = atomic64_add_return(npages, &mm->locked_vm);
        lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
-       if (locked > lock_limit && !capable(CAP_IPC_LOCK))
+       if (locked > lock_limit && !capable(CAP_IPC_LOCK)) {
                ret = -ENOMEM;
-       else
-               atomic64_add(npages, &mm->locked_vm);
-
-       pr_debug("[%d] RLIMIT_MEMLOCK +%ld %ld/%ld%s\n", current->pid,
-                       npages << PAGE_SHIFT,
-                       atomic64_read(&mm->locked_vm) << PAGE_SHIFT,
-                       rlimit(RLIMIT_MEMLOCK),
-                       ret ? " - exceeded" : "");
+               atomic64_sub(npages, &mm->locked_vm);
+       }
 
-       up_write(&mm->mmap_sem);
+       pr_debug("[%d] RLIMIT_MEMLOCK +%ld %lld/%lu%s\n", current->pid,
+                       npages << PAGE_SHIFT, locked << PAGE_SHIFT,
+                       lock_limit, ret ? " - exceeded" : "");
 
        return ret;
 }
 
 static void decrement_locked_vm(struct mm_struct *mm, long npages)
 {
+       s64 locked;
+
        if (!mm || !npages)
                return;
 
-       down_write(&mm->mmap_sem);
-       if (WARN_ON_ONCE(npages > atomic64_read(&mm->locked_vm)))
-               npages = atomic64_read(&mm->locked_vm);
-       atomic64_sub(npages, &mm->locked_vm);
-       pr_debug("[%d] RLIMIT_MEMLOCK -%ld %ld/%ld\n", current->pid,
-                       npages << PAGE_SHIFT,
-                       atomic64_read(&mm->locked_vm) << PAGE_SHIFT,
+       locked = atomic64_sub_return(npages, &mm->locked_vm);
+       WARN_ON_ONCE(locked < 0);
+       pr_debug("[%d] RLIMIT_MEMLOCK -%ld %lld/%lu\n", current->pid,
+                       npages << PAGE_SHIFT, locked << PAGE_SHIFT,
                        rlimit(RLIMIT_MEMLOCK));
-       up_write(&mm->mmap_sem);
 }
 
 /*
-- 
2.21.0