[dm-devel] [PATCH v3 2/4] brd: extend the rcu regions to cover read and write

[Mikulas Patocka]

This patch extends the rcu regions, so that lookup followed by a read or
write of a page is done inside rcu read lock. This is needed for the
following patch that enables discard.

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

---
 drivers/block/brd.c |    8 ++++++++
 1 file changed, 8 insertions(+)

Index: linux-2.6/drivers/block/brd.c
===================================================================
--- linux-2.6.orig/drivers/block/brd.c
+++ linux-2.6/drivers/block/brd.c
@@ -150,23 +150,27 @@ static void copy_to_brd(struct brd_devic
        size_t copy;
 
        copy = min_t(size_t, n, PAGE_SIZE - offset);
+       rcu_read_lock();
        page = brd_lookup_page(brd, sector);
        BUG_ON(!page);
 
        dst = kmap_atomic(page);
        memcpy(dst + offset, src, copy);
        kunmap_atomic(dst);
+       rcu_read_unlock();
 
        if (copy < n) {
                src += copy;
                sector += copy >> SECTOR_SHIFT;
                copy = n - copy;
+               rcu_read_lock();
                page = brd_lookup_page(brd, sector);
                BUG_ON(!page);
 
                dst = kmap_atomic(page);
                memcpy(dst, src, copy);
                kunmap_atomic(dst);
+               rcu_read_unlock();
        }
 }
 
@@ -182,6 +186,7 @@ static void copy_from_brd(void *dst, str
        size_t copy;
 
        copy = min_t(size_t, n, PAGE_SIZE - offset);
+       rcu_read_lock();
        page = brd_lookup_page(brd, sector);
        if (page) {
                src = kmap_atomic(page);
@@ -189,11 +194,13 @@ static void copy_from_brd(void *dst, str
                kunmap_atomic(src);
        } else
                memset(dst, 0, copy);
+       rcu_read_unlock();
 
        if (copy < n) {
                dst += copy;
                sector += copy >> SECTOR_SHIFT;
                copy = n - copy;
+               rcu_read_lock();
                page = brd_lookup_page(brd, sector);
                if (page) {
                        src = kmap_atomic(page);
@@ -201,6 +208,7 @@ static void copy_from_brd(void *dst, str
                        kunmap_atomic(src);
                } else
                        memset(dst, 0, copy);
+               rcu_read_unlock();
        }
 }
 

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