mm: make mm->pinned_vm an atomic64 counter

Taking a sleeping lock to _only_ increment a variable is quite the
overkill, and pretty much all users do this. Furthermore, some drivers
(ie: infiniband and scif) that need pinned semantics can go to quite
some trouble to actually delay via workqueue (un)accounting for pinned
pages when not possible to acquire it.

By making the counter atomic we no longer need to hold the mmap_sem and
can simply some code around it for pinned_vm users. The counter is 64-bit
such that we need not worry about overflows such as rdma user input
controlled from userspace.

Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Christoph Lameter <cl@linux.com>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

3 files changed, 9 insertions, 9 deletions

diff --git a/drivers/infiniband/hw/hfi1/user_pages.c b/drivers/infiniband/hw/hfi1/user_pages.c
index e341e6dcc388..40a6e434190f 100644
--- a/drivers/infiniband/hw/hfi1/user_pages.c
+++ b/drivers/infiniband/hw/hfi1/user_pages.c
@@ -92,7 +92,7 @@ bool hfi1_can_pin_pages(struct hfi1_devdata *dd, struct mm_struct *mm,
 	size = DIV_ROUND_UP(size, PAGE_SIZE);
 
 	down_read(&mm->mmap_sem);
-	pinned = mm->pinned_vm;
+	pinned = atomic64_read(&mm->pinned_vm);
 	up_read(&mm->mmap_sem);
 
 	/* First, check the absolute limit against all pinned pages. */
@@ -112,7 +112,7 @@ int hfi1_acquire_user_pages(struct mm_struct *mm, unsigned long vaddr, size_t np
 		return ret;
 
 	down_write(&mm->mmap_sem);
-	mm->pinned_vm += ret;
+	atomic64_add(ret, &mm->pinned_vm);
 	up_write(&mm->mmap_sem);
 
 	return ret;
@@ -131,7 +131,7 @@ void hfi1_release_user_pages(struct mm_struct *mm, struct page **p,
 
 	if (mm) { /* during close after signal, mm can be NULL */
 		down_write(&mm->mmap_sem);
-		mm->pinned_vm -= npages;
+		atomic64_sub(npages, &mm->pinned_vm);
 		up_write(&mm->mmap_sem);
 	}
 }
diff --git a/drivers/infiniband/hw/qib/qib_user_pages.c b/drivers/infiniband/hw/qib/qib_user_pages.c
index 075f09fb7ce3..c6c81022d313 100644
--- a/drivers/infiniband/hw/qib/qib_user_pages.c
+++ b/drivers/infiniband/hw/qib/qib_user_pages.c
@@ -75,7 +75,7 @@ static int __qib_get_user_pages(unsigned long start_page, size_t num_pages,
 			goto bail_release;
 	}
 
-	current->mm->pinned_vm += num_pages;
+	atomic64_add(num_pages, &current->mm->pinned_vm);
 
 	ret = 0;
 	goto bail;
@@ -156,7 +156,7 @@ void qib_release_user_pages(struct page **p, size_t num_pages)
 	__qib_release_user_pages(p, num_pages, 1);
 
 	if (current->mm) {
-		current->mm->pinned_vm -= num_pages;
+		atomic64_sub(num_pages, &current->mm->pinned_vm);
 		up_write(&current->mm->mmap_sem);
 	}
 }
diff --git a/drivers/infiniband/hw/usnic/usnic_uiom.c b/drivers/infiniband/hw/usnic/usnic_uiom.c
index ce01a59fccc4..854436a2b437 100644
--- a/drivers/infiniband/hw/usnic/usnic_uiom.c
+++ b/drivers/infiniband/hw/usnic/usnic_uiom.c
@@ -129,7 +129,7 @@ static int usnic_uiom_get_pages(unsigned long addr, size_t size, int writable,
 	uiomr->owning_mm = mm = current->mm;
 	down_write(&mm->mmap_sem);
 
-	locked = npages + current->mm->pinned_vm;
+	locked = npages + atomic64_read(&current->mm->pinned_vm);
 	lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
 
 	if ((locked > lock_limit) && !capable(CAP_IPC_LOCK)) {
@@ -187,7 +187,7 @@ out:
 	if (ret < 0)
 		usnic_uiom_put_pages(chunk_list, 0);
 	else {
-		mm->pinned_vm = locked;
+		atomic64_set(&mm->pinned_vm, locked);
 		mmgrab(uiomr->owning_mm);
 	}
 
@@ -441,7 +441,7 @@ static void usnic_uiom_release_defer(struct work_struct *work)
 		container_of(work, struct usnic_uiom_reg, work);
 
 	down_write(&uiomr->owning_mm->mmap_sem);
-	uiomr->owning_mm->pinned_vm -= usnic_uiom_num_pages(uiomr);
+	atomic64_sub(usnic_uiom_num_pages(uiomr), &uiomr->owning_mm->pinned_vm);
 	up_write(&uiomr->owning_mm->mmap_sem);
 
 	__usnic_uiom_release_tail(uiomr);
@@ -469,7 +469,7 @@ void usnic_uiom_reg_release(struct usnic_uiom_reg *uiomr,
 	} else {
 		down_write(&uiomr->owning_mm->mmap_sem);
 	}
-	uiomr->owning_mm->pinned_vm -= usnic_uiom_num_pages(uiomr);
+	atomic64_sub(usnic_uiom_num_pages(uiomr), &uiomr->owning_mm->pinned_vm);
 	up_write(&uiomr->owning_mm->mmap_sem);
 
 	__usnic_uiom_release_tail(uiomr);