[PATCH 5/6] powerpc/mmu: 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: Andrew Morton <a...@linux-foundation.org>
Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org>
Cc: Christoph Lameter <c...@linux.com>
Cc: Davidlohr Bueso <d...@stgolabs.net>
Cc: Michael Ellerman <m...@ellerman.id.au>
Cc: Paul Mackerras <pau...@samba.org>
Cc: <linux...@kvack.org>
Cc: <linuxppc-dev@lists.ozlabs.org>
Cc: <linux-ker...@vger.kernel.org>
---
 arch/powerpc/mm/mmu_context_iommu.c | 27 +++++++++++----------------
 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/arch/powerpc/mm/mmu_context_iommu.c 
b/arch/powerpc/mm/mmu_context_iommu.c
index 8038ac24a312..a4ef22b67c07 100644
--- a/arch/powerpc/mm/mmu_context_iommu.c
+++ b/arch/powerpc/mm/mmu_context_iommu.c
@@ -54,34 +54,29 @@ struct mm_iommu_table_group_mem_t {
 static long mm_iommu_adjust_locked_vm(struct mm_struct *mm,
                unsigned long npages, bool incr)
 {
-       long ret = 0, locked, lock_limit;
+       long ret = 0;
+       unsigned long lock_limit;
        s64 locked_vm;
 
        if (!npages)
                return 0;
 
-       down_write(&mm->mmap_sem);
-       locked_vm = atomic64_read(&mm->locked_vm);
        if (incr) {
-               locked = locked_vm + npages;
                lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
-               if (locked > lock_limit && !capable(CAP_IPC_LOCK))
+               locked_vm = atomic64_add_return(npages, &mm->locked_vm);
+               if (locked_vm > lock_limit && !capable(CAP_IPC_LOCK)) {
                        ret = -ENOMEM;
-               else
-                       atomic64_add(npages, &mm->locked_vm);
+                       atomic64_sub(npages, &mm->locked_vm);
+               }
        } else {
-               if (WARN_ON_ONCE(npages > locked_vm))
-                       npages = locked_vm;
-               atomic64_sub(npages, &mm->locked_vm);
+               locked_vm = atomic64_sub_return(npages, &mm->locked_vm);
+               WARN_ON_ONCE(locked_vm < 0);
        }
 
-       pr_debug("[%d] RLIMIT_MEMLOCK HASH64 %c%ld %ld/%ld\n",
-                       current ? current->pid : 0,
-                       incr ? '+' : '-',
-                       npages << PAGE_SHIFT,
-                       atomic64_read(&mm->locked_vm) << PAGE_SHIFT,
+       pr_debug("[%d] RLIMIT_MEMLOCK HASH64 %c%lu %lld/%lu\n",
+                       current ? current->pid : 0, incr ? '+' : '-',
+                       npages << PAGE_SHIFT, locked_vm << PAGE_SHIFT,
                        rlimit(RLIMIT_MEMLOCK));
-       up_write(&mm->mmap_sem);
 
        return ret;
 }
-- 
2.21.0