The brd driver is the only in-tree driver that may sleep currently.
After some discussion on linux-fsdevel, we decided that any driver
may choose to sleep in its ->direct_access method.  To ensure that all
callers of bdev_direct_access() are prepared for this, add a call
to might_sleep().

Signed-off-by: Matthew Wilcox <[email protected]>
---
 fs/block_dev.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 0bb2993..1982437 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -446,6 +446,12 @@ long bdev_direct_access(struct block_device *bdev, 
sector_t sector,
        long avail;
        const struct block_device_operations *ops = bdev->bd_disk->fops;
 
+       /*
+        * The device driver is allowed to sleep, in order to make the
+        * memory directly accessible.
+        */
+       might_sleep();
+
        if (size < 0)
                return size;
        if (!ops->direct_access)
-- 
2.1.4

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