linux-kernel - [PATCH 4/6] drivers/IB,hfi1: do not se mmap

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Date:   Mon, 21 Jan 2019 09:42:18 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     akpm@...ux-foundation.org
Cc:     dledford@...hat.com, jgg@...lanox.com, jack@...e.de,
        ira.weiny@...el.com, linux-rdma@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        dave@...olabs.net, mike.marciniszyn@...el.com,
        dennis.dalessandro@...el.com, Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 4/6] drivers/IB,hfi1: do not se mmap_sem

This driver already uses gup_fast() and thus we can just drop
the mmap_sem protection around the pinned_vm counter. Note that
the window between when hfi1_can_pin_pages() is called and the
actual counter is incremented remains the same as mmap_sem was
_only_ used for when ->pinned_vm was touched.

Cc: mike.marciniszyn@...el.com
Cc: dennis.dalessandro@...el.com
Reviewed-by: Ira Weiny <ira.weiny@...el.com>
Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 drivers/infiniband/hw/hfi1/user_pages.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/drivers/infiniband/hw/hfi1/user_pages.c b/drivers/infiniband/hw/hfi1/user_pages.c
index 40a6e434190f..24b592c6522e 100644
--- a/drivers/infiniband/hw/hfi1/user_pages.c
+++ b/drivers/infiniband/hw/hfi1/user_pages.c
@@ -91,9 +91,7 @@ bool hfi1_can_pin_pages(struct hfi1_devdata *dd, struct mm_struct *mm,
 	/* Convert to number of pages */
 	size = DIV_ROUND_UP(size, PAGE_SIZE);
 
-	down_read(&mm->mmap_sem);
 	pinned = atomic64_read(&mm->pinned_vm);
-	up_read(&mm->mmap_sem);
 
 	/* First, check the absolute limit against all pinned pages. */
 	if (pinned + npages >= ulimit && !can_lock)
@@ -111,9 +109,7 @@ int hfi1_acquire_user_pages(struct mm_struct *mm, unsigned long vaddr, size_t np
 	if (ret < 0)
 		return ret;
 
-	down_write(&mm->mmap_sem);
 	atomic64_add(ret, &mm->pinned_vm);
-	up_write(&mm->mmap_sem);
 
 	return ret;
 }
@@ -130,8 +126,6 @@ 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);
 		atomic64_sub(npages, &mm->pinned_vm);
-		up_write(&mm->mmap_sem);
 	}
 }
-- 
2.16.4