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

Davidlohr Bueso
2019-01-21T17:43:19Z

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.weiny@intel.com>
Signed-off-by: Davidlohr Bueso <dbueso@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