sample: vfio-mdev: avoid deadlock in mdev_access()

mdev_access() calls mbochs_get_page() with mdev_state->ops_lock held,
while mbochs_get_page() locks the mutex by itself.
It leads to unavoidable deadlock.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

diff --git a/samples/vfio-mdev/mbochs.c b/samples/vfio-mdev/mbochs.c
index d5d5a499160c106427592e809cd7955b947fcd55..2535c3677c7b66a1650fc3a1a7fb9c99684ae8ea 100644 (file)
--- a/samples/vfio-mdev/mbochs.c
+++ b/samples/vfio-mdev/mbochs.c
@@ -178,6 +178,8 @@ static const char *vbe_name(u32 index)
        return "(invalid)";
 }
 
+static struct page *__mbochs_get_page(struct mdev_state *mdev_state,
+                                     pgoff_t pgoff);
 static struct page *mbochs_get_page(struct mdev_state *mdev_state,
                                    pgoff_t pgoff);
 
@@ -394,7 +396,7 @@ static ssize_t mdev_access(struct mdev_device *mdev, char *buf, size_t count,
                   MBOCHS_MEMORY_BAR_OFFSET + mdev_state->memsize) {
                pos -= MBOCHS_MMIO_BAR_OFFSET;
                poff = pos & ~PAGE_MASK;
-               pg = mbochs_get_page(mdev_state, pos >> PAGE_SHIFT);
+               pg = __mbochs_get_page(mdev_state, pos >> PAGE_SHIFT);
                map = kmap(pg);
                if (is_write)
                        memcpy(map + poff, buf, count);