[PATCH 6/6] drivers/IB,core: reduce scope of mmap_sem

[Davidlohr Bueso]

ib_umem_get() uses gup_longterm() and relies on the lock to
stabilze the vma_list, so we cannot really get rid of mmap_sem
altogether, but now that the counter is atomic, we can get of
some complexity that mmap_sem brings with only pinned_vm.

Reviewed-by: Ira Weiny <ira.we...@intel.com>
Signed-off-by: Davidlohr Bueso <dbu...@suse.de>
---
 drivers/infiniband/core/umem.c | 41 ++---------------------------------------
 1 file changed, 2 insertions(+), 39 deletions(-)

diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index 678abe1afcba..b69d3efa8712 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -165,15 +165,12 @@ struct ib_umem *ib_umem_get(struct ib_udata *udata, 
unsigned long addr,
 
        lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
 
-       down_write(&mm->mmap_sem);
-       new_pinned = atomic64_read(&mm->pinned_vm) + npages;
+       new_pinned = atomic64_add_return(npages, &mm->pinned_vm);
        if (new_pinned > lock_limit && !capable(CAP_IPC_LOCK)) {
-               up_write(&mm->mmap_sem);
+               atomic64_sub(npages, &mm->pinned_vm);
                ret = -ENOMEM;
                goto out;
        }
-       atomic64_set(&mm->pinned_vm, new_pinned);
-       up_write(&mm->mmap_sem);
 
        cur_base = addr & PAGE_MASK;
 
@@ -233,9 +230,7 @@ struct ib_umem *ib_umem_get(struct ib_udata *udata, 
unsigned long addr,
 umem_release:
        __ib_umem_release(context->device, umem, 0);
 vma:
-       down_write(&mm->mmap_sem);
        atomic64_sub(ib_umem_num_pages(umem), &mm->pinned_vm);
-       up_write(&mm->mmap_sem);
 out:
        if (vma_list)
                free_page((unsigned long) vma_list);
@@ -258,25 +253,12 @@ static void __ib_umem_release_tail(struct ib_umem *umem)
                kfree(umem);
 }
 
-static void ib_umem_release_defer(struct work_struct *work)
-{
-       struct ib_umem *umem = container_of(work, struct ib_umem, work);
-
-       down_write(&umem->owning_mm->mmap_sem);
-       atomic64_sub(ib_umem_num_pages(umem), &umem->owning_mm->pinned_vm);
-       up_write(&umem->owning_mm->mmap_sem);
-
-       __ib_umem_release_tail(umem);
-}
-
 /**
  * ib_umem_release - release memory pinned with ib_umem_get
  * @umem: umem struct to release
  */
 void ib_umem_release(struct ib_umem *umem)
 {
-       struct ib_ucontext *context = umem->context;
-
        if (umem->is_odp) {
                ib_umem_odp_release(to_ib_umem_odp(umem));
                __ib_umem_release_tail(umem);
@@ -285,26 +267,7 @@ void ib_umem_release(struct ib_umem *umem)
 
        __ib_umem_release(umem->context->device, umem, 1);
 
-       /*
-        * We may be called with the mm's mmap_sem already held.  This
-        * can happen when a userspace munmap() is the call that drops
-        * the last reference to our file and calls our release
-        * method.  If there are memory regions to destroy, we'll end
-        * up here and not be able to take the mmap_sem.  In that case
-        * we defer the vm_locked accounting a workqueue.
-        */
-       if (context->closing) {
-               if (!down_write_trylock(&umem->owning_mm->mmap_sem)) {
-                       INIT_WORK(&umem->work, ib_umem_release_defer);
-                       queue_work(ib_wq, &umem->work);
-                       return;
-               }
-       } else {
-               down_write(&umem->owning_mm->mmap_sem);
-       }
        atomic64_sub(ib_umem_num_pages(umem), &umem->owning_mm->pinned_vm);
-       up_write(&umem->owning_mm->mmap_sem);
-
        __ib_umem_release_tail(umem);
 }
 EXPORT_SYMBOL(ib_umem_release);
-- 
2.16.4