[PATCH 2/3] qcow2: Assert that qcow2_cache_get() callers hold s->lock

[Kevin Wolf]

qcow2_cache_do_get() requires that s->lock is locked because it can
yield between picking a cache entry and actually taking ownership of it
by setting offset and increasing the reference count.

Add an assertion to make sure the caller really holds the lock. The
function can be called outside of coroutine context, where bdrv_pread
and flushes become synchronous operations. The lock cannot and need not
be taken in this case.

Signed-off-by: Kevin Wolf <address@hidden>
---
 block/qcow2-cache.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c
index d29b038a67..75b13dad99 100644
--- a/block/qcow2-cache.c
+++ b/block/qcow2-cache.c
@@ -327,6 +327,9 @@ static int qcow2_cache_do_get(BlockDriverState *bs, 
Qcow2Cache *c,
     int min_lru_index = -1;
 
     assert(offset != 0);
+    if (qemu_in_coroutine()) {
+        qemu_co_mutex_assert_locked(&s->lock);
+    }
 
     trace_qcow2_cache_get(qemu_coroutine_self(), c == s->l2_table_cache,
                           offset, read_from_disk);
@@ -386,6 +389,8 @@ static int qcow2_cache_do_get(BlockDriverState *bs, 
Qcow2Cache *c,
         }
     }
 
+    assert(c->entries[i].ref == 0);
+    assert(c->entries[i].offset == 0);
     c->entries[i].offset = offset;
 
     /* And return the right table */
-- 
2.20.1