[PATCH 2/4] brd: extend rcu read sections

[Mikulas Patocka]

This patch extends rcu read sections, so that all manipulations of the
page and its data are within read sections.

This patch is a prerequisite for discarding pages using rcu.

Note that the page pointer escapes the rcu section in the function
brd_direct_access, however, direct access is not supposed to race with
discard.

Signed-off-by: Mikulas Patocka <mpato...@redhat.com>

---
 drivers/block/brd.c |   19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

Index: linux-2.6/drivers/block/brd.c
===================================================================
--- linux-2.6.orig/drivers/block/brd.c
+++ linux-2.6/drivers/block/brd.c
@@ -71,10 +71,8 @@ static struct page *brd_lookup_page(stru
         * safe here (we don't have total exclusion from radix tree updates
         * here, only deletes).
         */
-       rcu_read_lock();
        idx = sector >> PAGE_SECTORS_SHIFT; /* sector to page index */
        page = radix_tree_lookup(&brd->brd_pages, idx);
-       rcu_read_unlock();
 
        BUG_ON(page && page->index != idx);
 
@@ -92,7 +90,12 @@ static struct page *brd_insert_page(stru
        struct page *page;
        gfp_t gfp_flags;
 
+       rcu_read_lock();
+
        page = brd_lookup_page(brd, sector);
+
+       rcu_read_unlock();
+
        if (page)
                return page;
 
@@ -151,9 +154,13 @@ static void brd_zero_page(struct brd_dev
 {
        struct page *page;
 
+       rcu_read_lock();
+
        page = brd_lookup_page(brd, sector);
        if (page)
                clear_highpage(page);
+
+       rcu_read_unlock();
 }
 
 /*
@@ -246,6 +253,8 @@ static void copy_to_brd(struct brd_devic
        unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
        size_t copy;
 
+       rcu_read_lock();
+
        copy = min_t(size_t, n, PAGE_SIZE - offset);
        page = brd_lookup_page(brd, sector);
        BUG_ON(!page);
@@ -265,6 +274,8 @@ static void copy_to_brd(struct brd_devic
                memcpy(dst, src, copy);
                kunmap_atomic(dst);
        }
+
+       rcu_read_unlock();
 }
 
 /*
@@ -278,6 +289,8 @@ static void copy_from_brd(void *dst, str
        unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
        size_t copy;
 
+       rcu_read_lock();
+
        copy = min_t(size_t, n, PAGE_SIZE - offset);
        page = brd_lookup_page(brd, sector);
        if (page) {
@@ -299,6 +312,8 @@ static void copy_from_brd(void *dst, str
                } else
                        memset(dst, 0, copy);
        }
+
+       rcu_read_unlock();
 }
 
 /*

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