Btrfs: kmap_atomic(KM_USER0) is safe for btrfs_readpage_end_io_hook

None of the checksum verification code schedules, so we can use the faster
kmap_atomic

Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index cdb7011..8adfe05 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1748,7 +1748,7 @@ static int btrfs_readpage_end_io_hook(struct page *page, u64 start, u64 end,
        } else {
                ret = get_state_private(io_tree, start, &private);
        }
-       kaddr = kmap(page);
+       kaddr = kmap_atomic(page, KM_USER0);
        if (ret)
                goto zeroit;
 
@@ -1757,7 +1757,7 @@ static int btrfs_readpage_end_io_hook(struct page *page, u64 start, u64 end,
        if (csum != private)
                goto zeroit;
 
-       kunmap(page);
+       kunmap_atomic(kaddr, KM_USER0);
 good:
        /* if the io failure tree for this inode is non-empty,
         * check to see if we've recovered from a failed IO
@@ -1772,7 +1772,7 @@ zeroit:
               (unsigned long long)private);
        memset(kaddr + offset, 1, end - start + 1);
        flush_dcache_page(page);
-       kunmap(page);
+       kunmap_atomic(kaddr, KM_USER0);
        if (private == 0)
                return 0;
        return -EIO;