linux-kernel - [PATCH v3 1/5] vduse: Remove unnecessary spin lock protection

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Message-Id: <20220720044144.90-2-xieyongji@bytedance.com>
Date:   Wed, 20 Jul 2022 12:41:40 +0800
From:   Xie Yongji <xieyongji@...edance.com>
To:     mst@...hat.com, jasowang@...hat.com, xiaodong.liu@...el.com,
        maxime.coquelin@...hat.com, stefanha@...hat.com
Cc:     songmuchun@...edance.com,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3 1/5] vduse: Remove unnecessary spin lock protection

Now we use domain->iotlb_lock to protect two different
variables: domain->bounce_maps->bounce_page and
domain->iotlb. But for domain->bounce_maps->bounce_page,
we actually don't need any synchronization between
vduse_domain_get_bounce_page() and vduse_domain_free_bounce_pages()
since vduse_domain_get_bounce_page() will only be called in
page fault handler and vduse_domain_free_bounce_pages() will
be called during file release.

So let's remove the unnecessary spin lock protection in
vduse_domain_get_bounce_page(). Then the usage of
domain->iotlb_lock could be more clear: the lock will be
only used to protect the domain->iotlb.

Signed-off-by: Xie Yongji <xieyongji@...edance.com>
---
 drivers/vdpa/vdpa_user/iova_domain.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/vdpa/vdpa_user/iova_domain.c b/drivers/vdpa/vdpa_user/iova_domain.c
index 6daa3978d290..bca1f0b8850c 100644
--- a/drivers/vdpa/vdpa_user/iova_domain.c
+++ b/drivers/vdpa/vdpa_user/iova_domain.c
@@ -211,17 +211,14 @@ static struct page *
 vduse_domain_get_bounce_page(struct vduse_iova_domain *domain, u64 iova)
 {
 	struct vduse_bounce_map *map;
-	struct page *page = NULL;
+	struct page *page;

-	spin_lock(&domain->iotlb_lock);
 	map = &domain->bounce_maps[iova >> PAGE_SHIFT];
 	if (!map->bounce_page)
-		goto out;
+		return NULL;

 	page = map->bounce_page;
 	get_page(page);
-out:
-	spin_unlock(&domain->iotlb_lock);

 	return page;
 }
-- 
2.20.1